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THE PROFESSIONAL MAGAZINE FOR ELECTRONICS AND COMPUTER SERVICING

G1E01'1101118S rvicing & Technology MAY 1994/$3.00

Servicing TV standby circuits

Camcorder servicing

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ContentsVolume 14, No. 5 May 1994

TOYOKE

0442

TOOLS &TOOPJ ASESHOWCASE

page 19

FEATURES7 Equipping the consumer electron-

ics service center for computerservicing: Parts 1 and 2By David PresnellAlthough you probably have most ofthe tools, test equipment, and knowl-edge that you need to service per-sonal computers, this two-part arti-cle lets you see what else you'll need.Part 1 deals with learning aboutcomputers, obtaining the equipmentand developing an approach to diag-nosis and service. Part 2 covers spe-cific solutions to specific problems.

20 Camcorder servicingBy The ES&T StaffBased on the Hitachi VM-2400video camcorder, this feature high-lights the functions of some of thecircuits that are unique to cam-corders, while emphasizing the

power circuits and also describessome possible failure modes causedby problems in the power circuits.

22 Servicing TV standby circuitsBy Homer DavidsonIn order for remote -control TV setsto be able to be switched on usingthe remote control transmitter, the

THE PROFESSIONAL MAGAZINE FOR ELECTRON AM) COMPUTER SERVICING

ELEGT1101110Servicing & Technology

remote receiver on the set must bepowered, even when the set is off.The standby power circuits providethe voltage necessary. When thesecircuits develop problems, this arti-cle can help.

ADVERTISINGSUPPLEMENT42 Tools & Toolcases Showcase

When you're servicing today's high-ly sophisticated consumer electron-ics products, the right tools are indis-pensable. For that reason, we'repleased to provide this Tools andToolcases Showcase; to bring youmore information about these com-panies that can provide you with justthe tool you're looking for, or makeyou aware of one that you didn'tknow existed.

DEPARTMENTS2 Editorial

4 News

19 Business CornerPart 8 of the Total QualityManagement series

27 Test Your Electronics Knowledge

28 Products

31 Profax

48 Books

49 Sams Photofacts

50 What Do You Know AboutElectronics?

54 Video CornerUnderstanding the CRT numberingsystem

55 Computer CornerA local bus primer

63 Literature

64 Correction

66 Classifieds/Readers' Exchange

68 Advertisers' Index

ON THE COVERFalling hardware prices and an increas-ing array of software for consumerapplications have contributed to theincreasing appearance of computers inhomes. Some study, and acquisition ofdiagnostic software and a few pieces ofcomputer -specific test equipment, canprepare the consumer electronics ser-vice center to service these products.(Photo courtesy of 3M)

May 1994 Electronic Servicing & Technology 1

Editorial

Rethinkingservice

Most consumer electronics servicingtechnicians service down to the compo-nent level. There are several good reasonsfor that. In the early days of consumerelectronics (read radio and TV, and vac-uum tubes) products were constructed onunified chassis. All of the componentsand sockets were mounted on the singlechassis and wired to each other with wireand solder. There were no modules thatcould be removed and replaced. If a tech-nician wanted to get a defective productworking again, he had to find the badcomponent(s) and replace them.

As technology in consumer electronicsadvanced, some products were designedin modular fashion. In some cases withthese products it made sense to exchangemodules to get the product back up andrunning. But in many cases, even thoughthe product was designed to be modular,and to be repaired by replacing modules,it was more cost effective to service to thecomponent level.

For one thing, many of these moduleswere very expensive. Service centers feltthat it was wrong of them to charge a cus-tomer to replace a several hundred dollarmodule when they could use a few teststo find the defective resistor or transistoron the printed circuit board. Not only that,but the cost to maintain an inventory ofmodules might severely tax the financialsituation of a small to medium size ser-vice center.

For many reasons, including those,consumer electronics servicing techni-cians tend to have a mindset that the cor-rect way to service a product is to find thecomponent or components that havefailed and replace them.

One of the other reasons that techni-cians prefer to troubleshoot to the com-ponent level is the sheer intellectual chal-lenge. For the same types of reasons thatsome people do crossword puzzles orindulge in other mental challenges, tech-nicians just want to demonstrate to them-selves and others that they can solve aproblem to its most fundamental cause.

Anyone who understands consumerelectronics and the technicians who keepthe products operating, applauds that atti-tude. It's admirable that these technicianswant very much to exercise their skills,and at the same time to save their cus-tomers and themselves money.

In some areas of consumer electronicstoday, however, things are changing;notably in the area of computers. IBM andcompatible computers are one hundredpercent modular. One of these units isassembled by piecing together a mother-board, a video card, disk drive controllers,the disk drives, a printer controller, amouse controller, and a power supplymodule, among other things.

Because of intense competition amongsuppliers, many of these modules areextremely inexpensive. A power supplymay cost around $60.00. A video cardwill typically cost less than $100.00. Eventhe motherboard will probably cost just afew hundred dollars.

Because of these extremely low mod-ule prices, in many cases it simply doesn'tmake sense to troubleshoot to the com-ponent level. How much time can a tech-nician spend troubleshooting, locating areplacement component and installingthe new component, when the cost of areplacement for the module is $60.00?

When faced with some of these newerproducts, a consumer electronics centerthat is steeped in the venerable traditionof service to the component level, needsto reevaluate its approach to service, inorder to be sure in every individual casethat it is servicing the product in the mostefficient, cost effective manner.

Keep those articles comingThe editorial in the July 1993 issue

mentioned to readers that we're con-stantly looking for good solid technicalarticles. Many readers responded and wehave recently published articles writtenby them. Several of those who sent arti-cles to us in response to that invitation arenow regular authors. Thanks, guys, andkeep them coming. We could use more!

The pace of change in consumer elec-tronics is continuing to accelerate. If youcan provide us with articles that explainhow some of this new technology works,or how to service it, especially TV andvideo, write or call me at P.O. Box 12487,Overland Park, KS 66282-2487; 913-492-4857. I'll get a copy of our writers'guidelines out to you immediately.

2 Electronic Servicing & Technology May 1994

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NewsSatellite from space trade show

The ProShow, a live satellite deliveredaudio program for satellite dealers andelectronic technicians, announces itsspring topic line-up. Scheduled dates in-clude: May 1, Tools of the Trade; May 8,Servicing What You Sell and Selling YourService; May 15, Troubleshooting Tricksand Tips; May 22, InterAssociation Co-operation; May 29, Service Centers-When to Farm Out the Work.

Each Sunday night, the ProShow re-volves around a particular topic. Often,the show features interviews from expertson the topic, but the majority of time isdevoted to callers.

"The topic gives us a starting point, butit is really the callers who determine thecontent of each show," explains ProShowhost Fred deFerbrache. "One caller cantouch off an important or pressing issueand the rest of the show moves in thatdirection. It is really the listener's show.I just get it started and answer the calls."

The first portion of The ProShow in-cludes a short prepared newscast. This de-livers the fast breaking stories that impacton the satellite and electronics industry.

"The ProShow is a powerful way to getnews and information to the industry. Be-sides having the immediacy of radio, itpools the experience of its listeners," com-mented Dick Glass, the president of SDAand ETA -I. "In this way, the listeners be-come the eyes and ears of the industry."

The first ProShow aired on October18th, 1992. It is produced in conjunctionwith the national Satellite Dealers Asso-ciation and the Electronics TechniciansAssociation, International by ElectronicsProfessionals, Inc. It can be heard on theOmega Radio Network (Galaxy 3, Chan-nel 17 at 5.8MHz) every Sunday nightfrom 9:00 pm to 11:00 pm EST. The call -in phone number is 219-293-9664. Deal-ers are encouraged to set up a VCR in theirstores to automatically record the show.

TVs score high inserviceability inspection

The International Society of CertifiedElectronics Technicians (ISCET) has be-gun conducting inspections of electronicproducts that have not been authorized by

the manufacturers of that product.In its second ISCET sponsored Ser-

viceability inspection, two televisionswere inspected at the Florida ElectronicService Convention, January 14, 1994, inJacksonville. The Goldstar Model GCT2054S scored an 84.48% for a good rat-ing. The Samsung Model TXB 2015/CXscored 85.29% which just slipped it intothe very good category.

Sets are rated on the criteria of productidentification, back removal, and re -in-stallation, preparation for and perfor-mance of in -home or minor in -shop ser-vice, preparation for and performance ofmajor bench servicing, and service dataconsiderations. Four other sets were ratedin August at the National ProfessionalElectronics Convention. All were rated asfair. Even though these inspections werenot authorized by the manufacturer, somemanufacturers have chosen to purchasetheir reports following the inspections.

The Serviceability program is a jointeffort among the manufacturers, the tech-nicians, and ISCET to improve productserviceability in the future. A manufac-turer can schedule a confidential inspec-tion at his selected site by contacting theISCET office.

Computer case settled out of courtAn independent computer service deal-

er, unable to afford the expenses of a Su-preme Court trial, has agreed to the termsof a computer manufacturer. Part of theterms was an agreement to not competewith that manufacturer for the service ofits products or any peripheral equipment.

Peak Computer Corp., the independentservice company, was sued by MAI Sys-tems Inc., a computer manufacturerturned servicer, for alleged violations ofthe U.S. Copyright Act. MAI says that thesoftware that operates its computers isonly licensed to the people who boughtand own the computers and that onlythose owners who are licensed may turnthe computer on. They charged that Peak-and any other independent servicecompany not approved or licensed byMAI-may not turn the computer on forservice without breaking the law. Theycontend-and two lower courts agreed-

that, when a computer is turned on, a"copy" of the operating program is madeinto the computer's RAM, and that thisviolates § 117 of the U.S. Copyright Act.The latest decision was rendered in theNinth U.S. circuit court of Appeals inCalifornia.

The case was appealed to the SupremeCourt in 1993 and the application wasaccepted. However, the service dealer'sbusiness liability insurance was, effec-tively, canceled and trials were imminent-ly pending to award damages based uponthe Ninth Circuit Court's decision. Un-able to afford the substantial penalties orthe legal fees for the appeal, Peak owner,Vince Chiechi, was forced to capitulate tothe MAI-offered settlement. In return forMAI not enforcing a judgement that couldhave called for as much as a million dol-lars, Peak allegedly agreed not to serviceor maintain any of MAI's computers andto not solicit any of MAI's customers forthe repair or maintenance of any periph-eral equipment.

With this settlement, the decision of theNinth Circuit Court has now become thelaw of the Ninth Circuit. However, othercases based on the same premise are pend-ing around the country. NESDA andNIAS officials, who consider the decisionby the Circuit Court to have created an"intolerable legal situation," are reason-ably sure that one or more of these caseswill ultimately reach the Supreme Court.

In the meantime, NESDA is continu-ing its efforts to establish a legal fund, theService Industry Signal (SIS), based uponvoluntary contributions from indepen-dent service industry professionals andsupporters. Such a fund would permitNESDA to (1) file additional Friend ofthe Court briefs in the Supreme Court asneeded; (2) promote legislation to aidindependent servicers in obtaining repairparts and service manuals from appliance,computer, and consumer electronicsmanufacturers; and (3) possibly renderassistance to a financially strapped inde-pendent that is caught up in a precedent -setting case (such as Peak).

NESDA is asking all affected servicedealers and technicians and their associ-ations to contribute to the "S.I.S." legal


THE PROFESS/0.1AI PAAGADNE FOR ELECTRONICS AND COmmitER SERvCING

ELECTRONICServicing & Technology

Electronic Servicing & Technology is edited for ser-vicing professionals who service consumer electronicsequipment. This includes service technicians, field ser-

vice personnel and avid servicing enthusiasts who repair

and maintain audio, video, computer and other con-sumer electronics equipment.

EDITORIALNils Conrad Persson, EditorLinda Romanello, Assistant Editor

CONSULTING EDITORSHomer L.Davidson, TV Servicing ConsultantVictor Meeldijk, Components ConsultantJohn E. Shepler, Audio ConsultantSam Wilson, Electronics Theory Consultant

PRODUCTIONElizabeth Ryan, Art DirectorBarbara Terzo, Assistant Art DirectorSusan Reale, ArtistEdmond Pesonen, Electronic Composition Mgr.Dorothy Kehrwieder, Production ManagerEmily Kreutz, Advertising ProductionPat Le Blanc, Phototypographer

BUSINESSRichard A. Ross, PublisherJohn Dorr, General ManagerFrank V. Fuzia, ControllerCatherine Ross, Circulation DirectorMelissa Nitschke, Data Processing ManagerCarol Licata, Data ProcessingDenise Pyne, Customer Service

SALES OFFICEElectronic Servicing & Technology76 N. Broadway, Hicksville, NY 11801516-681-2922; FAX 516-681-2926

Diane G. Klusner, Director of AdvertisingEmily Kreutz, Sales Assistant

EDITORIAL CORRESPONDENCE:P.O. Box 12487Overland Park, KS 66212913-492-4857

Solve lb

NESDA AeMember, Electronic Servicing Audit Bureau of Circulations

Dealers Association Mombor

0'1 AFSPAop. INTERNAnoNot

ASSOCIATION FOR SERVICESMANAGEMENT INTERNATIONAL

Electronic Servicing & Technology (ISSN 0278-9922)is published 13 times a year by CO Communications,Inc. 76 N. Broadway, Hicksville, NY 11801. Telephone(516) 681-2922. Second class postage paid atHicksville, NY and additional offices. Subscriptionprices (payable in US dollars only): Domestic-oneyear $24.75, two years $45. Foreign countries-oneyear $30.75, two years $57. Entire contents copyright1994 by CO Communications, Inc. Electronic Servicing& Technology or CO Communications, Inc. assumes noresponsibility for unsolicited manuscripts. Allow sixweeks for delivery of first issue and for change ofaddress. Printed in the United States of America.

Postmaster: Please send change of address notice toElectronic Servicing & Technology, 76 N. Broadway,Hicksville, NY 11801.

CO Communications, Inc. is publisher of CO The RadioAmateur's Journal, Popular Communications, Micro -Computer Journal, CO Radio Amateur (Spanish CO), COAmateur Radio Equipment Buyer's Guide, CO AmateurRadio Beginner's Buyer's Guide. Popular Communica-tions Communications Guide, and Electronic Servicing& Technology.

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defense fund. Contributions may be sentto: SIS Fund, do NESDA, 2708 W. BerrySt., Fort Worth TX 76109, or call 817-921-9061.

Forty-four vendors to sponsorfiber optic training conference

Forty-four vendors of fiber optic prod-ucts have joined together to sponsor"Fiber U," the second annual Fiber OpticInstallers' Conference July 25 through

28, 1994 in Long Beach, CA. The confer-ence will include a combination of twen-ty-five classroom seminars and hundredsof hands-on workshops, plus the buildingof a demonstration fiber optic cable net-work as part of the training program forinstallers and users of fiber optics.

Fiber optics has become a householdword recently, since its enormous band-width makes it ideal for the backbone ofthe planned "national information infra-

B+K Precision introduces five new AC or Battery Powered Frequency Counters,with bandwidths ranging from 100MHz to 2.4GHz, time base stabilities from 2 to0.5 parts per million, and introductory prices from $209 to $499.

Model 1803C offers outstanding value for a 100MHz counter and is ideal fora wide range of applications. Model 1806 adds period and totalize functions forlow frequency applications, while Model 1807 has 1.3GHz bandwidth and an ul-tra -stable 0.5PPM TCXO time base with an optional accessory antenna. It is idealfor adjusting RF transmitters to FCC Standards. Model 1856A measures up to2.4GHz for personal communications service applications.

Get the performance and features you need and pay no more than you haveto, thanks to the intelligent new frequency counters available from B+K Precision!

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structure." To allow the mass deploymentof fiber throughout the country, moretrained installers are needed quickly.

"Fiber U" is the only hands-on trainingconference for fiber optics. It began inNashville, Tennessee in 1993 as a way forvendors of fiber optic products to train alarge number of installers conveniently.Two hundred attendees came to Nashvilleand participated in 18 seminars and 90hands-on workshops.

At the Long Beach Conference, a com-plete fiber optic network will be built, us-ing virtually every type of fiber opticcomponent, by the attendees as part oftheir training. Attendees will be trained onthe network, pulling cables through con-duit, splicing and terminating and testinginstalled cables in a realistic setting.

The 44 sponsors represent every typeof fiber optic products needed for in-stalling and maintaining any type of net-work. To make the installation even morerealistic, several networks will be operat-ing on the network during the conference,including a video surveillance system forconference security.

For more information on the confer-ence, contact Louise Downing, Confer-ence Coordinator, at Fotec. 800 -50 -FIBER,Fax 617-241-8616, email 541-0037 @MCImail.

DSS installationsThe Satellite Dealers Association has

learned that the business owned by SDASecretary Greg Woods has been commis-sioned by Thomson Consumer Electronicsto install the first working Digital SatelliteSystems (DSS). These initial (severaldozen) systems, used in what is called"beta testing," will provide user informa-tion back to Thomson, from actual homeenvironments. It will also give statisticsvital to ascertaining the total job ofinstalling the DSS 18 -inch dishes, wiringand instructing users as to operation.

Technicians employed by "TheSatellite Shop," operated by Woods outof Whitestown, IN, will be gaining directexperience in this installation and testingprogram. Users being equipped withsome of the initial production of DSShardware are primarily V.I.P.s associatedwith TCE in the central Indiana area.

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Equipping the consumerelectronics service center forcomputer servicingPart 1-Learning about computers, obtaining the equipment anddeveloping an approach to diagnosis and service.

By David Presnell

Au electronic equipment is subject tomalfunction at any time. This is true ofthe IBM computer and its clones, as wellas TVs, VCRs and other consumer elec-tronics products. The rapid growth of thelow-cost computer has resulted in the saleof millions of these systems over the lastfew years. Many consumers buy theirnew computer systems at discount cen-ters, mail-order houses, and other placesthat don't specialize in computers. Com-puter sales have become an add-on prod-uct line to department stores, home appli-ance centers, and hardware stores. Thesebusinesses often know little about thecomputers they sell.

Computer service for these computersis usually offered by a subcontractingfirm, typically offering a one-year on -siteservice agreement. Once this service con-tract has expired, the computer user turnsto local suppliers for service. The firststop is usually their favorite consumerelectronics service center. Buyers of thenew low-cost computers are often not fa-miliar with how to use their new com-puters, much less how to fix many of thesimple problems and conflicts that occur.

This article will look into some of themany common problems that arise with-in the computer. It will look at both hard-ware and software problems and suggestsome simple ways to troubleshoot them.To get started in computer service asquickly as possible, it is best, at first, toswap out defective mother boards, I/Ocards, and power supplies, for workingones, rather than attempt to diagnosedown to the component level. Actually,in many cases, because of the low cost ofreplacements and the high cost of a tech-nician's time, board or module level ser-

Presnell is owner of an independent computer ser-vicing business and a freelance technical writer

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Figure 1. When you take the cover off of a typical IBM compatible computer, (power off of course),you'll find something that looks like this. This is the mother board.

vice makes sense even for the experi-enced technician.

A good addition to your businessSuppose you service TV's and VCR's

for a living, and one day you receive a callfrom a good customer asking you to lookat his computer. You reply "I'm sorry butI don't work on computers, and I don'tknow anyone around here who does."Later, you may find out that the problemwas nothing more than a fuse, and that acompany 50 miles away charged them$75.00 to replace it. You could have re-

placed that fuse and saved your customera costly trip out of town.

Why are so many people afraid of com-puters? Computers are no harder to workon than any other electronic equipment.In fact, with a little knowledge, they'reeasier. Does a sick VCR diagnose itself?With the proper software, a computer can.

Start by learning computer operationWhat will you need to know before

adding computer service to your bench?The best advice I can give here is to obtaina computer. Buy one, rent one, use one at


CHECK THESEFOUR DIODES

IF SUPPLYIS SHORTED

(KEEPS BLOWING FUSES)

SOLDERED4N FUSE

Figure 2. The power supply has a soldered -in fuse that will required a soldering iron for replacement. If the power supply keeps blowing fuses.check the condition of the four diodes.

the public library, or borrow a friend's.An IBM compatible XT or AT with a harddrive will do nicely. It needs to have MS-DOS (version 5.0 or above) loaded as theprimary operating system. There is a ver-sion 6.0 out, but 5.0 will serve your needs.

Once you have a computer, sit down infront of it with the MS-DOS manual inhand and learn DOS. You can never be-come proficient as a computer servicetechnician until you learn at least the fun-damentals of MS-DOS. In fact, you willneed to understand the basic operation ofa computer, the basic parts of the comput-er, and DOS before you will obtain anyreal benefit from this or any other com-puter service article. Don't despair, it's easy.

Sit down with your computer opera-tor's manual and learn the basics. Takethe cover off (power off of course) andexplore. Locate the mother board (Figure1), floppy disk, hard disk, I/O cards, pow-er cables, keyboard plug, monitor card,power supply. Locate the fuse coming outof the back of the power supply, if it hasone there, and any batteries mounted onthe mother board. As with any modernelectronics circuits, use care inside. Be-fore you handle chips or other parts, puton a static wrist strap. Think before youact. Common sense will take you a long

way in computer service. And remember,you cannot take anything regarding com-puters as an absolute. When I'm absolute-ly sure, then I'm usually wrong. Keep thatbit of advice in mind as you begin to workon computers.

The tools of the tradeYou probably have most of the hard-

ware and tools you will need to servicecomputers. I should mention the impor-tance of high quality tools-they're farless expensive in the long run. Apart fromthe basic hand tools, hex wrenches, andother goodies, you may need a good den-tal probe set, and a good pair of medicalquality tweezers. A good U-shaped chippuller will come in handy for socketedDIP chips. I carry a portable soldering kit(butane type) to remove soldered -inCMOS RAM batteries and fuses in thefield (Figures 1 and 2). They're light andportable, and you don't have to worryabout static zapping the mother boardfrom the tip. If you buy a butane -poweredportable soldering iron, get the smallesttip you can obtain.

In the field, I carry a good DMM witha continuity beeper, and a 100MHz logicprobe. It's easy to acquire more than youneed, so regarding your computer service

bench, keep it trim. I would strongly sug-gest an isolation transformer for switch-ing -power -supply service. If you plan toservice monitors, you will need a servicebench similar to the one you use for TVservice. With the proper schematics, anygood TV technician can service monitors,so this article will concentrate on the com-puter itself. See Table 1 for a complete listof tools, accessories and test equipmentyou should have for personal computerservicing.

Replacement partsBuy parts only as you need them, espe-

cially if you're just starting. You can ac-quire a fortune in boards and chips thatyou'll rarely ever use. If you find somegood suppliers, you can often obtain com-puter parts overnight for a modest addi-tional shipping fee. You can and will ac-quire old computers for parts in the be-ginning. However, it's only fair to chargeused prices for used parts.

Servicing softwareYour major investment will be in com-

puter servicing software and firmware.Servicing software consists of diagnosticprograms on floppy disks that will helpyou locate the computer's problem(s).


Firmware includes plug-in cards andchips that will help you diagnose prob-lems when the computer won't boot.

You will need an MS-DOS boot disk(or system disk) with you. This disk willoften allow you to start up the computerwhen there's a problem with the harddrive that won't allow the computer toboot. Few computer owners can even findtheir manual, much less the original DOSdisk that came with the computer. On theboot disk that you carry with you, you willalso want the following DOS files:BACKUP, RESTORE, SYS, CHKDSK,EDIT, QBASIC, HELP, DEBUG, DISK -COPY, FORMAT, MIRROR, SETVER,UNDELETE, UNFORMAT, XCOPY,and any other DOS files that you thinkwill assist you in the field.

If you're familiar with DOS, you willknow that the above files are from MS-DOS 5.0 and will have to be placed on ahigh density 1.2MB floppy in order to fitthem all on. You should also have a bootdisk of the MS-DOS 3.2 (orclose version)for older XT systems. I carry one bootdisk of each for all four sizes of floppydisk. You should obtain these operatingsystems from the software supplier ofyour choice.

You will also need to obtain your diag-

Table 1

TOOLS AND TEST EQUIPMENTStandard toolsStandard electronic servicing test

equipmentElectrostatic discharge preventative

wrist strapDental probesTweezersIC pullerPortable soldering ironLogic probeIsolation transformerService literature/schematics

SOFTWAREDOS boot disk (system disk) with other

DOS programs on itDiagnostic software and firmware

utilities

BOOKSDOS manualOperating software manualsDiagnostic software/firmware manuals

KEYBOARDPLUG

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4

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Figure 3. The back of the computer has provisions for connection to the power line, and all ofthe peripherals. If you encounter a dead computer and you determine that there is power at theplug, check to see if the power cord and monitor cord are plugged in well, and that the 110/220switch is in the correct position.

nostic software. I use diagnostics fromLandmark Research. See the listing at theend of this article for addresses. You canpurchase direct or from many supplierssuch as Jensen Tools. I recommend thatyou obtain one of each of the followingtypes of software programs: XT servicediagnostics; 286 service diagnostics; 386service diagnostics; 486 service diagnos-tics; a general diagnostic program, and ahard disk diagnostic program. Also use-ful is a program called DOS UTILS fromOntrack Computer Systems, or a utilitiesprogram from another supplier.

Another type of product I suggest ob-taining is a POST reader card, that willhelp you diagnose the problem when thecomputer fails to boot. Also, you maywant to obtain a set of ROM POST (pow-er -on self test) chips for XT, AT -singlechip, and AT double chip ROMs. Whena computer won't boot, it cannot recog-nize the operating system, thus, it cannot

use diagnostic software. These POSTproducts are basically operating systemindependent. With them you can often de-termine the problem when a computerwon't boot. The ROM POST chips re-place the mother boards ROM chips andproduce standard POST codes. Fromthese codes or beeps, you can look in themanual and determine the problem area.

You can expect to invest around $2500for all the diagnostic items mentioned.You can also try out the many sharewareproducts (with caution) on the market.One of those I recommend is IBM ATDisaster Prevention or a similar productava-lable from any good source of share-ware. This program and like products willcapture and store the ATs current CMOSsetup settings to a floppy disk file, andwhen the need arises, will restore that fileto CMOS RAM. You might try a recog-nized shareware company such as TheSoftware Labs (their disk 495).


Using diagnostic softwareBefore you attempt to use any of the di-

agnostic software and firmware men-tioned above, read all the manuals and di-rections that come with the diagnostics.Once you've read them, read them again.As a computer technician, you must un-derstand the tools you're using before youuse them.

When you've read through everythingat least twice, write protect all of youroriginal disks then make backup copiesof all the disks you've received. You mayeven want to make a couple of copies ofeach-one for the field, and one for thebench. Remember to use low densitydisks for any programs that will be usedon XTs or PS2 25s. I put anything that willfit (not all of the programs will) on lowdensity disks, both 51/4 and 31/2. That way

the disks will work on both high and lowdensity drives. Put your originals away ina safe place.

Next, write protect your copies. Thiswould include placing the small blacktape tab from your label sheet over thenotch of a 51/4 disk, and sliding open thetab on a 31/2 disk. Why write protectthem? Imagine picking up a nasty com-puter virus from a customer's computerand transferring it to a dozen more com-puters before someone realizes that youare the cause of wiping out the data ontheir hard disk. Write protecting yourdisks protects you and your customers.

Now that you've learned your comput-er, learned DOS, studied your diagnosticsdocumentation, made backup disks, andwrite protected everything, proceed to sitdown with your diagnostics (both soft and

firm), and learn how to use them. Usecare, and read through your manual as youproceed at the keyboard.

If you have any data on your hard disk,I would suggest you back it up beforeusing any of the diagnostic programs.Most of them can and will lose your dataif you make mistakes, which is especial-ly likely while you're learning. This willalso be good experience for you. If it's atall possible, always back up your custom-er's data before performing potentiallydestructive procedures.

Once the hard drive is backed up cor-rectly, you can run all of the diagnosticsmany times through until you becomecomfortable with them, even to the pointof reformatting the hard disk. I will ref-erence many of these procedures withinthis article, but space won't allow for me

PROBLEMComputer works correctlyexcept when running aspecific program

Computer operates normallywith floppy disk butoperates incorrectly ornot at all with hard disk

Computer locks up or giveserror messages duringoperation of some programs

Monitor problems

Dead computer atturn -on

Table 2

POSSIBLE CAUSESoftware

CMOS RAM setup, the harddisk, or the disk controllercard. If the problem is causedby the hard disk it may be eithera bad program (such asCOMMAND.COM) on the disk,a mechanical problem with thedisk, or both.

Messages such as "not enoughmemory" may indicate thatprogram has used all availablememory, or that extended orexpanded memory managersare not operating as they shouldbe (computer is set up wrong).When small programs are runand such a message appears inDOS, the cause may be a badmemory chip.

Bad monitor or improper setup

Bad power supply, bad powercable, burned/broken foilson motherboard.

SOLUTIONCheck setup. Change if necessary. Ortry reinstalling program

If the computer boots okay off of thefloppy but will not recognize thehard disk, then the problem is mostlikely a dead CMOS battery if thecomputer is an AT. Check the batteryand replace it if necessary, then runsetup.If the computer is an XT, theproblem is most likely a bad controller card.

Check for bad software or viruses. Iflockups occur randomly within anyprogram or even when no applicationprogram is running, check for a faulton the motherboard

If monitor display was bad immediatelyon turn -on, check monitor. If monitorwas good on turn -on, but became wrongafter startup procedure, check startupfile for problem. Set up VGA or possiblyCMOS RAM.

Check visual and audible indicationssuch as lights, fans, disk driveoperation. Check power supply.Check power cable connections.Check outlets. Check motherboard foils


to explain the operation of each function.Also, if you are going to perform a de-structive procedure, such as formatting,always backup before proceeding.

Diagnostic approach

Computer problems can be divided intothree major categories:

software problems: hardware problems: and combined problems.

This article will explore each of thesethree areas. Just as with any other serviceproblem, many are not related to the prod-uct at all, but are caused by some exter-nal problem. We will first look at com-mon problems unrelated to the product.

If you're called out to service a deadcomputer, first consider the most likelycause. Check the outlet to see if it haspower. Follow the power cord to the surgeprotector. (If the computer doesn't have asurge protector then it's your duty to sellthe customer one.) Is the surge protectorlight on? Is the breaker tripped (or fuseblown) on the surge protector? If you'renot sure, test the outlets on the strip witha meter.

If all is well, continue on to the back ofthe computer. Are the power and monitorcords plugged in securely? Is the 110V/220V switch in the correct position (Fig-ure 3)? If the computer has an externalscrew -in type fuse, check it. If it's blown,try a replacement if you have one. If itblows again, you've already located thegeneral problem area: the power supply.

If the computer seems to be working,but the monitor is blank, check the con-trols in front and rear of the monitor, espe-cially the brightness. You will be sur-prised at how many calls you will get forwhich the problem is nothing more thana brightness control turned down.

If the keyboard is not working, turn itupside down and check the AT/XT switchif it has one. Make sure the switch is inthe proper position. Also, make sure thekeyboard is plugged in correctly.

At this point, question the customer.Find out all you can about how the com-puter was acting before the trouble oc-curred. Who has been using it?

Did they hear anything unusual, smellanything, or notice that the computer hasnot been working right for several days?

Just as a doctor asks you "where ithurts," you must determine from your

customer as much as you can about theproblem and how it occurred. Has thecomputer been moved recently. Have newprograms been installed. Has anythingbeen done differently. I responded to aservice call in which the customer told meover the phone that he thought his com-puter had a virus. When I arrived, I ques-tioned him regarding symptoms.

As I began, I noticed that there was anarea of lost data on his hard disk thatcrossed several files, mostly on the bootsector of the drive. While I worked heasked me the tell -tale question: "Do youthink that dropping the computer couldhave caused it?" He informed me that hehad just moved it downstairs and haddropped it about six steps from the bot-tom of the stairs. Yes, bouncing comput-ers can cause hard disk problems.

That brings up another point. Manycomputer users know little about theirmachines. You must treat your customerswith kid gloves if you want repeat busi-ness. This customer was very embar-rassed to tell me what really happened.My response was to proceed to recover asmuch data as possible, reformat the harddisk, (locking out had sectors), then re-load his data and programs. All worked

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well! He was very happy. He had alreadyaccepted in his mind that the computerhad to be replaced. I kept my opinions tomyself about how to handle a computer.

Determining where the problem isThe toughest part of the computer tech-

nician's job is to determine whether theproblem is software (the programs), hard-ware (the boards, chips, cords, and con-nectors), or a combination of the two.

You must take your time, and use care-ful consideration in this process. Here iswhere digital theory can be of use. For allpractical purposes, however, I have de-vised a simple method to determine whicharea to concentrate on. The followingquestions will help you determine wheth-er software or hardware problems exist,or a combination of both.

Does the computer work correctlyexcept when running a specific program?If so, this is most likely a software prob-lem. Try re -installing the program thatcauses the problem. If you're familiarwith the program, check the setup. Theprogram may simply be set up incorrectly.

Does the computer operate normally

off of a floppy disk but refuse to operatecorrectly or at all while trying to use thehard disk? This symptom suggests a prob-lem with either the CMOS RAM setup, thehard disk, or the disk controller card. If theproblem is caused by the hard disk it maybe either a bad program (such as COM-MAND.COM) on the disk, a mechanicalproblem with the disk, or both. If the com-puter boots okay off of the floppy but willnot recognize the hard disk, then the prob-lem is most likely a dead CMOS battery ifthe computer is an AT. Check the batteryand replace it if necessary, then run setup.If the computer is an XT, the problem ismost likely a bad controller card.

Does the computer lock up or give er-ror messages during operation of any pro-gram? Messages such as "not enoughmemory" may simply indicate that theprogram has used all of the memory thatis available, or that extended or expand-ed memory managers are not operating asthey should be (computer is set up wrong).However, when small programs are runand such a message appears in DOS, thecause may be a bad memory chip. Lock-up can be caused by bad software or virus-es, but if lockups occur randomly within

any program or even when no applicationprogram is running, suspect a fault on themotherboard as the most likely cause.

Monitor problems are self evident justas are common TV problems. However,monitor problems could be caused by themonitor, the display card located on themother board, connecting cables, or achip on the mother board. Improper setupof a VGA monitor can cause some effectsthat may be seen as problems by some.When you turned the computer on, wasthe problem immediate, or did it start onlyafter the computer had completed its start-up routine? If the monitor was okay tostart with, but became wrong only afterthe computer completed the start-up, youprobably have to do nothing more than setup the VGA controller or possibly theCMOS RAM.

Does the computer seem dead whenturned on? After checking the basics men-tioned above (checking power, etc.), lookto see if the power light on the computercase is working. What about the monitorpower on light? Are all the switches on?Place a floppy disk in drive A and type A:then press ENTER. Does the floppy diskdri ve light up? Can you hear the disk drive

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working? Can you hear the power supplyfan working? See Table 2 for a table ofthese steps.

Going through these five basic stepswill not fix the computer, but will helpyou determine which diagnostic ap-proach to take. The basic idea is to deter-mine what is working and to temporarilydiscount that area as the problem area. Asyou continue to see what works or re-

sponds to a given action, your directionwill become more clear. You will also not-ice what does not work or respond as itshould, and this will lead you to place thecorrect diagnostic disk in the drive, installfirmware as needed, or take the comput-er back to the bench for more advanced study.

Many corrective procedures may be ef-fected with nothing more than typing afew keys on the keyboard. Remember, a

Part 2-Specific solutions to specific problems

Part 1 of this article, "Learning aboutcomputers, obtaining the equipment anddeveloping an approach to diagnosis andservice," which appears on page seven ofthis issue, suggests an approach to learn-ing about personal computers and ob-taining the equipment and informationnecessary to service personal computers.This second part describes some commonproblems you will encounter in servicingpersonal computers and suggests an ap-proach to solving these specific problems.

Software problemsSoftware problems can be some of the

most frustrating problems to correct on acomputer. People will assume that you, asa computer technician, know all there isto know about every program they have.What customers don't realize is that thereare thousands of programs, and no humancould possibly know them all. If you havetime, try to learn all you can about asmany popular programs as you can. Allprograms produced by Microsoft aregood programs to learn. Popular pro-grams such as Word Perfect, Lotus 123,Quicken, MS -Windows, will certainlycross your path. It would be profitable foryou to learn as much as you can aboutthese programs.

I will look into various common soft-ware related problems and ways to try tocorrect them. First, let's consider theproblem of "missing data or files on thehard disk."

Restoring missing dataOne of the most likely and most fre-

quent causes of missing data is operatorerror. It's not unusual for a computerowner to format the non backed -up harddisk then call the technician to get theirdata back. Deleted and erased files areanother cause of missing data. If the cus-

tomer has done nothing after such mis-takes happen, recovery is often a simpleand painless process. However, if the cus-tomer has tried to fix it by copying overthese deleted areas, recovery may behopeless. If they happen to be using MS-DOS 5.0 or above, however, then all maynot be lost.

If a hard disk that's using MS-DOS 5.0or above has been accidentally formatted,then you can try the following: Boot thecomputer with an MS-DOS boot disk indrive A:. When the customer formattedthe disk, they may have been prompted toput a blank formatted disk in drive A: tosave DOS's mirror (UNFORMAT) infor-mation. If they did so, and have this disk,by all means use it. Unformat will use theinformation on the floppy to recover thedrive. If you have this unformat floppy,at the A: prompt (with the MS-DOS diskin drive A:) type UNFORMAT C:. Note:The floppy you booted from must containthe unformat and mirror related com-mands. See your MS-DOS manual formore information.

If you do not have this unformat flop-py disk, then at the A: prompt type UN -FORMAT C:/L. This command will tryto unformat the disk using any existinginformation in the root directory and fileallocation table (FAT). Follow on -screenprompts, and think before you press thatenter key. You may be able to recovermost non -fragmented files on the disk.

UndeletingDOS 5.0 and 6.0 also have a utility

called UNDELETE to be used when a filehas been accidentally deleted using theDEL or ERASE command. Check yourDOS manual for instructions on usingUNDELETE. For all practical purposes,I use DOSUTILS SCAN to attempt re-covery of deleted files as described below.

computer with MS-DOS is a powerfultool within itself. Pressing the right keyscan correct many problems without fur-ther assistance.

See the second part of this article, "Spe-cific solutions to specific problems,"below for information on how to diagnoseand correct common problems that youwill encounter in servicing personal com-puters.

If your customer is using a version ofDOS earlier than 5.0, you can probablyforget using DOS to attempt an unformator undelete. The first step might be to tryusing a file recovery utility. Insert the util-ities disk in drive A: and invoke the pro-gram. From the main menu select the filerecovery utility and follow on -screen in-structions. Although, the file recoveryutility may not recover a formatted disk,it will recover deleted files in most cases.There are also utilities available that willspend hours or even days trying to recov-er data from a formatted disk, however, Idon't own any of these programs.

Customers should have backed up theirdata on a regular basis. They should alsohave all of their original programs onfloppies. Thus, if neither unformat or filerecovery works, then proceed to installtheir programs back onto the hard disk,then load any data they may have backedup. One such incident will teach your cus-tomers a valuable lesson: backup data often.

If the customer's data is really valuable,and they have no backup, then you can re-move the hard disk and send it to specialtycompanies (listed in the back of comput-er magazines) and have them attempt torecover the data. Not many of your cus-tomers will want to pay the high cost ofsuch service (around $150 per hour).

Bad programsAnother common cause of missing data

is bad programs. Believe it or not, someprograms have small areas that simply donot work correctly. That's why softwaredevelopers often release X.01 correctedversions shortly after a new programcomes out. These areas can cause all kindsof problems. Also, programs can, forsome unknown reason, stop working or be-gin working in an unpredictable manner.

In these cases, first try re -installing the


program from the original disk. If the cus-tomer does not have the original, but hasan illegal copy, then this may be the prob-lem. Suggest they obtain a legal copyfrom their software supplier. You can al-ways try the software technical supportline for assistance. This number is usual-ly located on the inside cover of the user'smanual if the customer can find it.

VirusesAnother cause of missing data is virus-

es. Although, I think computer viruseshave been overplayed, they do exist. If thecomputer acts strange, try running ananti -virus program. If the operating sys-tem is MS-DOS 6.0, you can type MSAVto start Microsoft Anti -virus. You mighttry one of the many anti -virus programson the shareware market. Be sure to buyfrom a company that guarantees 100%virus free software.

Keep in mind that missing data is notalways missing. Look through the direc-tories and subdirectories on the hard disk.You may find the customer's data in aplace you never imagined. One word pro-cessor was saving all WP50 data files inthe DOS subdirectory just as it had beentold by the user, but when asked to loadone, WP50 couldn't find the file becauseit wasn't where it was supposed to be.

Another common problem is that the

Figure 4. If the computer is dead, turn the power off, remove the cover and locatethe power cables coming out of the power supply going to the boards and drivesof the computer. Use a DMM to check the voltages.

Figure 5. If the computer is dead, but the power supply has a correct +5v out-put, take a reading off of the yellow +12V line. This reading will normally be justabove or below +12v. If this line proves okay, then check downstream to seewhere the power stops.

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program won't start or run correctly. Themost common cause is that the programis set up wrong. You might try lookingthrough the pull down menus if the pro-gram has them. You may find the item thatneeds changing. The main menu may alsooffer ways in which to change or config-ure the system to work properly. As a lastresort, try re -installing the program fromthe original installation disk. This shouldget the program back to the default setupthat works best in most cases.

Cross -linked files/lost clustersAnother cause of software problems is

something called "Cross -linked files and/or lost clusters." This is often caused byturning off the computer while programsare running (abrupt power down). Youcan read about this problem in your MS-DOS manual. To correct these problems,DOS provides a tool called CHKDSK.CHKDSK can do a lot to help maintainyour computer's files. I type CHKDSK atthe C: prompt soon after I sit down at anycomputer.

This program will give you informa-tion about the size and available space ofboth the hard disk and memory. It will alsotell you if there are any cross -linked filesor lost clusters on the disk. When run bytyping CHKDSK, the program will onlyshow you what it found. However, if

CHKDSK showed problems, then if youtype CHKDSK/F, it will try to fix any lostclusters. CHKDSK is limited in that it willnot generally fix cross -linked files.

The simplest way to explain cross -linked files is that two programs havebecome intertwined. This problem occursin the FAT; and when it occurs, usuallyone or all of the involved files may haveto be deleted from the computer, then re-loaded if necessary later. At this point, usea utility program such as DOSUTILS.

ConflictsAnother common cause of programs

not running correctly is software or hard-ware conflicts. Some programs will notrun correctly when terminate -and -stay -resident (TSR) programs are running inthe background. To quickly see if a TSRprogram is causing the problem, boot thecomputer from a system floppy (withoutautoexec.bat and config.sys) in drive A.Then type C: and press enter to get intothe hard disk. Start the program and deter-mine if the problems still exist. By boot-ing from a clean floppy you can be surethat no TSR programs are running in thebackground. If this doesn't solve theproblem, there may be a hardware con-flict or even a true hardware fault.

Full software diagnostics starting witha program like PC PROBE would be in


order at this point. If all shows up okay,then begin looking at the root directoryand continue through each subdirectorylooking for files relating to the problemprogram. Files have a funny way of get-ting in the wrong place. Again, you maytry re -installing the software, or check itssetup. It's possible that a conflict existsbetween the program and the monitor(program not setup correctly for the typemonitor being used) or the printer.

Another common problem is trying touse certain DOS programs from the MS -Windows program. When you go to DOSwithout shutting Windows down, Win-dows is still running in the background(eating up memory). You have shelled outto DOS. You are not actually at the cleanDOS prompt. Many programs will notoperate properly when started from with-in another program, or while another pro-gram is running in the background.

Hardware problemsComputer hardware problems are not

as common as software problems, but youcan be sure that many of the millions ofpersonal computers now in use will devel-op a hardware problem at some point.

Dealing with a dead computerA common problem is the dead com-

puter. After checking the power cords tobe sure the computer is getting power, lis-ten for the operation of the fan (if the com-puter is equipped with one). Also checkto see if the power light is working. Whenyou turn on the switch, listen for a beepfrom the computer. If all this indicates adead computer, turn the power off, re-move the cover and locate the power ca-bles coming out of the power supply go-ing to the boards and drives of the computer.

When you look inside the computer,you may find an unused four -socket pow-er connector just lying to the side. If not,unplug one from one of the floppy diskdrives. If the plug is a small one, off of a3.5 -inch drive, you can insert a small barewire into the socket to hook your meterto. If you can find a standard four -socketplug, use it (see Figure 4). The meter'sprobes will fit nicely into its holes. Lookfor a connector with a red wire, two blackwires, and a yellow wire. Normally thered wire is +5V, the yellow +12V, and theblack wires are ground.

Take a meter reading from the red(+5V) to ground. You can attach the me - SONY

ter's ground lead to the metal case of thepower supply, but it's simpler and surerto attach both to the power connector. Setyour meter to read 5Vdc (or the next levelup). Turn on the computer. If the powersupply is working as it should, you willget a reading just under or just over +5V,depending upon the load placed on thepower supply by the other components.

If the power supply shows no output,then locate the fuse. If it's available exter-nally you should have already checked itwith the meter. Usually, you will have toremove the power supply cover to checkthe fuse. This will usually require you toremove the power supply from the case.You may wish to take the computer backto your bench at this point. If the fuse isblown, replace it with one of the correctsize and value. Power up the supply. Ifthis fuse blows, then the power supplywill have to be replaced.

You can obtain replacement suppliesand boards from many sources. A num-ber of them are listed at the end of thisarticle. Be sure to order the correct sizesupply for the case, and the same or high-er wattage. Different case styles use dif-ferent size supplies. Your supplier will beable to help you get the right size. You

should consider the cost of a new supplybefore spending too much time trying tofix an old one. Typically, supplies will runfrom $39.00 to $89.00 depending on thewattage, size, and whether the supply isUL listed or not. Always try to obtain aUL listed supply.

I must emphasize the importance ofchecking input power to the supply. If youhad the supply cover off to check the fuse,set your meter to 120Vac. Using the caseas ground, power up and carefully take areading on the line input side of the fuse(or the 120V line coming into the supply).If you don't measure an input voltage,check those cables again. Power cords doopen occasionally.

If the poker supply is producingthe correct voltages

If the power supply has a correct +5Voutput, take a reading off of the yellow+12V line. This reading will normally bejust above or below +12V. If this lineproves okay, then (power down) locatethe mother board power connectors P8and P9 (Figure 5). Make sure both of theseconnectors are seated firmly into themother board. These two connectors willalways be positioned so that the black

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ground lines (usually two or more) oneach connector are side by side.

On these connectors, most have a red+5V, yellow +12V, white -5V, (white is -

12V on some) and violet or blue -12V.You can insert a small length of bare wiredown each connector (where the wirefrom the power supply enters the back ofthe connector) you wish to check. Be surenot to short any two lines together.

Using the logic probeIf all the lines indicate correct voltages,

power down and hook up your logic probeaccording to its instructions. I usually op-erate mine from an independent +5V sup-ply. However, you can connect the blacklead to the power supply case, and the redlead to +5V at one of the power connec-tors +5V (red) lines. Use care at this point.Be sure to use precautions to avoid elec-trostatic discharge damage before pro-ceeding any further.

Once your probe is working, (you cantest it by touching the tip to any groundwith the power on), locate any DIP chipon the mother board. Look the chip up inone of the many reference manuals if youhave one. Locate the Vcc or other +5Vpin and carefully touch the probe tip tothis pin. Never short two pins with theprobe tip. (You can burn tiny foils on themotherboard.) All you are doing is tryingto determine if any voltage is getting tothe chips.

If you don't have a chip reference, justprobe each pin on the chip. If you lightthe probe with some highs and lows, thensome power is getting to this chip. Youcan locate and check other chips the sameway, but use care, especially with the sur-face mount (flat pack) chips. As you'reworking, look over the board to see if any-thing looks out of place. Also look forburned places on the board, especiallythose in close proximity to P8 and P9, themain power connectors. If power is notgetting to the chips, and the power sup-ply seems ok, you will probably need toreplace the mother board.

Power -on self -test

Many IBM compatibles produce aPOST (power on self test) when firstturned on. This POST performs a basicdiagnostic on the CPU, the RAM memo-ry, the I/O ports, and other hardware.Although limited, if POST finds a prob-lem, it may produce error codes on the

screen, or beeps from the computer'sspeaker, or both. It could mean nothingmore than a loose plug-in card or con-nector or a corrupted CMOS RAM. How-ever, it could indicate a faulty motherboard. Since POST codes vary widelyfrom manufacturer to manufacturer, it'sdifficult to determine what the beeps orcodes mean. You might look in the backof the books that came with your diag-nostic software. They list many POSTcodes from many of the most commonmanufacturers.

At this point, you've checked all wiringand connectors and found no shorts.You've made sure that all plug-in boardsare firmly seated into the mother board.Plug in a POST reader card (power off)and follow the manufacturer's directions.The codes displayed on the card shouldshow the problem. If not, the next step isto install the ROM POST chip(s) as out-lined in the instruction manual. If eitherof these diagnostics indicate the problem(probably with the mother board), pro-ceed to correct the problem, which is usu-ally a replacement of the mother board,I/O card, or re -setup of the computer'sCMOS RAM.

Try disconnecting the problemIf a computer is not working correctly,

generally beeping more than twice (may-be pausing then repeating the beeps), andfirmware diagnostics do not find the prob-lem, you might try a crude but effectiveprocedure that I use occasionally. Withthe computer off, unplug one item, thenturn the power back on to see if the beepremains. Power down, plug the item backin, then unplug another; then power backup and listen for the beep. This techniqueis both fast and effective.

I power down and start with the harddisk and floppy disk I/O card(s). Unplugthem from the mother board and listen tosee if the beeps stop or change. If they do,you may have found the fault. If the beepcontinues unchanged, then power downand plug them back in, and unplug themonitor card. Power up again to test.Continue this until all plug-in cards havebeen checked. This will often lead you tothe problem. You might even try unplug-ging the ROM chips, RAM chips, or mod-ules, any other plug-in chips, includingthe CPU (if a plug-in type).

Remember to power down, unplug,power up, see if any change occurred,

power down, then plug in the chip or mod-ule you removed. Also remember to usea static strap when removing or replacingchips. While the chip is out, place it on aconductive surface, such as the conduc-tive foam that static -sensitive ICs comein or a piece of aluminum foil. Never touchthe pins on any chip while it is removed.

Determining what's in the computerMost of the other computer hardware

problems will be such that the computerwill boot, but, it will not operate correct-ly when booted. Many problems relatedto hardware can be quickly located usingprograms that check the computer andprovide a readout of the computer's com-position, and diagnostics. My procedureis to place a disk with the diagnostic pro-gram PC PROBE in drive A: and attemptto start it from there. Using PC PROBE,the first thing you want to do is to look atthe system and to see what it is composedof. Under the Info menu item select "Sys-tem Info" and proceed to look at the sys-tem information that the software hasdetermined. For example, if the diagnos-tic software shows no hard disk when oneis present, you may have already foundthe problem. In this case, an indication ofno hard disk present, the CMOS backupbattery is probably dead or weak.

You might notice less memory indicat-ed than the computer has, thus meaning abad RAM chip. You might also notice thata monochrome monitor is indicated, whenyou're looking directly at a super VGAmonitor. If this is the case, the VGA BIOSchip may require setup, (usually a pro-gram located on the hard disk under a sub -directory such as TVGA or SVGA or VGA).

Using the diagnosticsIf this information does not indicate a

problem, select the diagnostics menu.You will start with "Select Test Mode,"or similar step, from the diagnostic menu.When open, this window will allow youto select single test or batch test. Try thesingle test first. Run all of the tests exceptthe memory test and the drive test. If noproblem shows up, run these tests again.If no problem shows up this time, run thememory test.

If after running these tests, no errors areindicated, then the problem is most like-ly a hard disk or software problem, or pos-sibly a CMOS SETUP problem. Run agood hard disk diagnostic program to


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check the hard disk. General diagnosticsare good to locate the problem area, whilespecific diagnostics will help pinpointand correct the problem.

If the hard disk diagnostic indicates thatthere are no problems with the disk dri-ves, then I will proceed to run service di-agnostics. Each of the service diagnosticdisks that I use is specific to a specificCPU. There is a separate disk for an XT,AT -286, 386, 486, or PS2. These diag-nostics are more specific than the gener-al diagnostic software, more technical,and generally more powerful. I use these

diagnostics to run extensive tests on thehardware. Service diagnostics also con-tain utilities that will pay for the programsin a short time. Some clone computershave a CMOS RAM that is difficult to setup using the built-in setup program. Ser-vice diagnostics has a utility that will doa nice job of setting up such a CMOSRAM. In fact, it can setup some segmentsof the CMOS that cannot be setup fromwithin some of the older on -chip setupprograms at all.

Software diagnostics and firmware willnot locate all problems, but you can be

sure many of them will be found easilywith the proper diagnostic software andfirmware tools.

Combined problemsCombined problems occur when both

software and hardware problems exist atthe same time. A hard disk controller cardmalfunction, for example, could alsocause damage to programs loaded on thehard disk. CMOS RAM setup problemsfrom a dead CMOS battery is also a com-bined problem. A crashed hard disk fromdropping the computer could have caused


severe mechanical damage, as well as fileand data loss.

You should approach the multi -symp-tom computer with a hardware first, soft-ware second approach. Get the hardwareworking so you can take a closer look atthe software.

Run your hardware diagnostics as nec-essary to locate and correct any hardwareproblems. For example: replace theCMOS battery; replace the controllercard; check the hard disk to see if badareas can be locked out; and recover anydata or replace the hard disk as the needmay be.

Now that you have any hardware prob-lems working to your satisfaction, pro-ceed to locate and correct any software

problems. If you have data loss, alwaystry to recover as much as you can beforeproceeding with a full or partial format.If some hardware problem has writtenover some EXE files, try reloading (or re-installing) them. With a little patience youcan restore the system to optimum per-formance with minimal loss of data inmost cases.

Putting it all togetherCommon sense will carry you a long

way in computer service. Learn all youcan about computers and DOS before youattempt service. Some could ask how any-one could learn or keep up with comput-ers or DOS as fast as they change. You

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can't really, but you can learn the basicsabout computers and DOS, then learnhow and where to locate the advanced in-formation when you need it.

For example, I carry a copy of the MS-DOS 5.0 manual as part of my field ser-vice kit. I also carry all of the diagnosticuser's manuals that came with my soft-ware and firmware diagnostics.

A few of my special customers haveprograms such as Word Perfect and Lotus123. I have reference manuals on theseprograms and others. When the callcomes in that "I can't get WP to print myenvelopes," I proceed to lug my WP ref-erence manual on site. I sit, read, and ex-periment, until I locate the problem.Guess what? The next time I encounterthat problem, I don't need the manual.That's called getting paid to learn.

To date, I've never had a customer com-plain about my looking it up in the book.In fact, many will seem amazed when youpull a 500 -page technical manual out ofyour service kit. In the background youoften hear comments like "that guy real-ly knows computers," all because I pulledout a manual. People are just about asafraid of books as they are of computers.

On my bench, I have a few spare moth-er boards, I/O cards, a couple of floppydisk drives, a spare monitor and card, anda couple of old hard drives that work.These parts are not for sale. I occasional-ly use them to check and see if my diag-nostics were correct. For example, yourdiagnostics indicates that the problemmay be the hard disk. It takes but a fewminutes to unplug the suspected hard disk(still mounted in the case) and plug itsconnectors (from the controller card andpower supply) to a known good harddrive. If the known working drive oper-ates with the system while the suspecteddrive did not, then you have truly locatedthe problem.

With a little care, you can take a knownworking mother board and carefully un-plug all necessary connectors and cardsfrom the suspect mother board (stillmounted in the computer case) and plugthem into the good one to see if every-thing else is working. If all else fails, justswap parts until the thing starts working.

As you can see, computer service is justlike all other service jobs. You do what-ever is necessary to fix it at the least costpossible. Computer service can be a prof-itable addition to your business.


Business Corner

This is the eighth part in the BusinessCorner series on W. Edwards Deming'sTotal Quality Management.

TQM Point 8Drive out fear so that everyone may

work effectively for the organization.Fear is one of the most destructive ofhuman emotions. Point 8 of the TQMphilosophy accurately maintains thatfear causes problems with both qualityand production in the workplace. On themanagement side, the notion of "jobsecurity" may allow a sense of paranoiato block the sharing of ideas or infor-mation. Many employees are oftenafraid to ask for instructions regardingtheir work, or to say that they need moreresources. Finally, fear of argument orreprimand often prevents employeesfrom talking openly about on-the-jobproblems.

Several years ago, an employee of aconsumer electronics service companyarrived at a customer site and, after sev-eral minutes realized that he didn't havethe parts needed to complete the serviceprocedure. Already behind scheduleand not wanting to tell his superior thathe hadn't packed the proper parts, hewrapped aluminum foil around theblown OEM fuse. After all, he hadalready endured a verbal reprimand forthe same type of oversight, and he real -

Ross is a technical writer and microcomputer consultantfor Ft. Hays State University, Hays. KS.

Will Total QualityManagement

work for youPart eight

I John Ross

ly did intend to return the next day withthe proper fuse.

Unfortunately, as often happens, theemployee didn't go back to the site be-cause of a heavy work schedule and per-sonal plans.

As you might already suspect, theoriginal intermittent power supplyproblem surfaced to start a fire in thecustomer's home. Not surprisingly, thecustomer sued the service company andthe employee lost his job. The publici-ty surrounding the case eventuallyforced the company to close its doors.Among other things, fear turned an eas-ily preventable situation into a horrorstory.

Abolishing fear in the workplace canand should be an everyday responsibil-ity for management. Several methodsthat address both employer and employ-ee fear exist. Certainly, avoiding on-the-job friendships might seem wise in thecontext of maintaining distance andpower. However, every employee expe-riences a wide range of personal prob-lems that may affect their job experi-ence. For managers and supervisors,having empathy for the human side ofemployees may be the first step towardbetter management and to providingsupport at the right time.

In the last "Business Corner" article,we saw how a person's position canblock the type of communication thatevery organization needs. The manag-er in that situation did not realize that

problems existed in his department.Crossing the informal and formal bar-riers that exist between supervisors andemployees often allows both parties togain an understanding of the roles thateach play. In some instances, managersor supervisors may want to join theiremployees as they work through theday. In other instances, managers or su-pervisors may want to involve their em-ployees in the decisions that affect thewell-being of the organization. Eachtype of occasion will provide opportu-nities for both the manager and theemployee to build a healthy workingrelationship and solid communications.

Unquestionably, ridding the work-place of fear can provide many advan-tages. From a purely financial point ofview, confident employees are moreproductive and efficient. As the "blownfuse" example shows, fear will oftenresult in some very tangible costs forboth the employer and the employee.Obviously, the employee lost his jobwhile the employer sacrificed money.The true long-term cost of fear, howev-er. cannot be measured. Fear, caused bya lack of understanding or closed -mind-ed attitudes, can feed irrational behav-ior and can breed disloyalty. In theexample, both individuals lost therespect of their peers and customers.Thus the incident teaches a crucial les-son. While a fearful employee neverstays long, a feared manager is not like-ly to prosper.


Camcorder servicingBy The ES&T Staff

For those who are new to camcorder ser-vicing, and for those who have been ser-vicing camcorders for some time, we'llstart with one basic statement: a cam-corder consists of both a camera and a vid-eocassette recorder. It's easier to under-stand and service these products if youcan get a picture of the camcorder as awhole, and appreciate just what a com-plex product it is. Its electronics and me-chanical systems are similar to those thatyou'd find in a VCR, and its optics arelike those that you'd find in any camera,and include the electronics circuitry andmechanical gadgets that adjust the opticsfor such functions as zoom, focus and au-tofocus. In addition, a camcorder alsocontains a small video monitor, called theelectronic viewfinder or EVF, that allowsthe user to see exactly what he's captur-ing on film.

Of course, there is an important subsetof circuitry that a VCR contains that acamcorder does not: a tuner.

It's impossible to do justice to cam-corder servicing in a relatively brief mag-azine article, so here's what this articlewill do:

explain the functions of some of thecircuits that are unique to camcorders,

emphasize the power circuits, anddescribe some of the possible failuremodes caused by problems in the powercircuits. This article will be based on theHitachi VM-2400 video camcorder. Seethe Profax schematic diagrams in this is-sue for the inside story on this camcorder.

The sensorOne of the problems in dealing with

new technology, such as camcorders, isthe difficulty that design engineers havein coming up with terminology that is de-scriptive of the functions performed by agiven component or circuit segment. So,engineers who work for different manu-facturers, even within "Japan, Inc.," maycall the same things by different names.

Or, even if they call things by the samename, the technical literature from dif-ferent manufacturers may place differentdegrees of emphasis on the terms.

For example, in the service manual forthe Hitachi VM-2400, the circuits andcomponents that are used to convert theimage formed by the camera lens into anelectrical signal and condition it so that itcan be processed by the signal processingcircuitry is called the "sensor." Flippingthrough the manuals of other manufac-turers showed that while some seemed tocall it the sensor, others either did not, orsimply did not employ that terminology.

Another possible source of confusionhere is that camcorders have, as do VCRs,other totally unrelated sensors, whichsense excessive moisture (dew sensor),the end of tape, and other conditions thatwarrant shutting down of the mechanisms.

In this camcorder, the "sensor" is theimage sensor, which primarily consists ofthe CCD imager (IC001), the sensor driv-er (IC005), the pre-process circuits (IC003)and other support circuitry. All of this cir-cuitry is located on the sensor PCB.

The CCDThe beginning of the entire process of

recording a scene using a camcorder is theconversion of a visual (light) image to anelectronic signal. In most consumer cam-corders, that's accomplished by using acharge -coupled device array (CCD). ACCD is a device that outputs an electricalsignal when light falls on it. A typical two-dimensional camcorder CCD array may

be able to generate thousands of pixels(picture elements).

The picture information signal gener-ated by the CCD is then transmitted to thepre-process IC where the video signal isconditioned and separated into the lumi-nance (brightness) and chrominance (col-or) signals.

These signals are sent to the processsection where they are processed, thenoutput to the main luminance/chromasection, then ultimately to the video headwhere they are recorded onto the tape.

Troubleshooting the camcorderIn any system as complex as a camcord-

er, there are literally hundreds of thingsthat can go wrong and cause improper op-eration. Some of these things may causelittle more than slight misadjustment ofthe color, or a little noise in the picture.Other things may cause the VCR to ceasefunctioning altogether.

In this article, we will focus on thepower generation and distribution cir-cuits in the camcorder. Here are somesteps to take when you run into a cam-corder problem.

Camcorder doesn't operate at allThe circuitry described here may be

found in this month's Profax.The power for a typical camcorder is

supplied either from a charged battery orfrom an external power supply. There isno power supply circuitry, as such, on acamcorder. That is, the circuitry that steps


down the ac line voltage rectifies and reg-ulates it. The camcorder is dc only.

When the operator is using the cam-corder in portable mode, the power comesfrom the battery. When the camcorder isplugged in, the power is dc from theadapter. The adapter is where the voltagetransformation, rectification and regula-tion take place.

Power for the various functions and cir-cuits of the camcorder takes a tortuousroute. The raw B+ comes either from thebattery, via the dc light control pc board,then via a 2A fuse to the system controlboard for distribution, or via the dc inputjack on the system control board, back tothe dc light control board, then via the 2Afuse back to the system control board.

In addition to appearing on the systemcontrol board, this unregulated 9.6V(A9.6V) is routed to the switching regu-lator, where it is used as a source for theregulator, which produces several regu-lated voltages which are used as supplieson the system control PC board, and/orfurther distributed to other circuitry with-in the camcorder.

The switching regulator also developsthe B+ for the capstan and cylinder. Thissignal is routed to the main servo printedcircuit board.

From there, the cylinder and capstanB+ are routed to the capstan motor drivepc hoard, and the cylinder B+ is routed tothe cylinder motor drive circuits.

The A9.6V is also routed to severalother boards, including the trouble sensorboard, and the process (encoder) circuitboard. From the process (encoder) circuitboard, the A9.6V is, in turn, routed to thedc -to -dc pc board. Here this voltage isused as a source of supply to generate allof the voltages for the camera section: C -8V. C I 5V, C9V and C5V.

When power supply problems occur ina camcorder, tracking down the problemand correcting it becomes to some extentan exercise in following circuit traces,and detective work.

Tracking down power problemsBased on this analysis, it's possible to

isolate power problems by performing alittle detective work. For example, if thecamcorder has power, and everythingseems to be operating, but when some orall of the camera functions, such as zoom,or focus, don't operate. there is likely aproblem with the dc -to -dc converter.

on the nomenclature

Here are some comments on the cam-corder schematic diagrams that mighthelp you navigate around the schematicsin this month's Profax while followingthe circuit descriptions in this article.

Connections among various printedcircuit boards is by means of variousplugs and connectors. Thus, on the sen-sor schematic diagram, there's a plug atthe lower left, PG002. The notation justbelow the plug says "to Process(Process) PG102". Below that is nota-tion [P5-14].

All of that information lets us knowthat this plug on the sensor printed cir-cuit board is connected to a plug on theprocess printed circuit board, and thatthe signal from this circuitry is input tothe process circuitry. This PC board, fur-thermore, plugs directly into the processPCB without benefit of an intermediateconnector. The notation [P5-14] informs

us that the process PC board will befound on page 5-14 of the manufactur-er's original document.

In cases where there is some kind ofconnector between pc boards, the dia-gram tells you that. In some cases, theconnector is permanently fastened toone of the boards and plugs on to theother board at the other end, and in somecases there are plugs on both boards andthe connector plugs at both ends.

For example, the dc -to -de converterboard in the VM-2400 has a perma-nently attached connector CN I DD (theDD standing for dc -to -dc), which plugsat the other end into PG107 on theProcess pc board. On the other hand, theprocess pc board has a plug PG104which connects to a plug on the autofo-cus board, PG06AF (AF for autofocus),via a connector that plugs into bothplugs, CN201 (CN for connector).

One possibility is that the A9.6V sourcevoltage is not arriving at the dc -to -dc con-verter input plug. Check at pin I ofCN1DD. If there is voltage here, one ofthe foils on the hoard may be burned orcracked, or one or more components onthe board may be faulty. If there is no volt-age at this point, trace the A9.6V circuithack until you find the point where thevoltage appears.

If only one of the camera functions isnot operating properly, the problem maybe that the motor that controls that func-tion is defective, or the voltage that con-trols that function may be absent. Checkthe input to the inoperative motor. If theinput is present. check the motor. If theinput is absent, track back to see where itdisappears.

Suppose the opposite is true. If the cam-era is totally dead, the main power is ei-ther not getting to the camera at all, or isbeing shortstopped somewhere. If thecamcorder is being operated on a battery,the obvious steps here are to check thebattery. operate the camcorder with a dif-ferent battery, or operate the camcorderusing the ac adaptor.

If the camcorder remains totally dead,

try tracing the power path. Check to seeif there is A9.6V at pin 4 of the dc con-trol board. If not, is the fuse blown? Ifthere is power here, check step by stepuntil you reach the inputs of the dc -to -dcconverter and the switching regulator.

Divide and conquerA camcorder is a complex device, but

its circuits are pretty much neatly divid-ed into functions, and the circuitry foreach function is grouped on a single cir-cuit board. The power circuit. on the otherhand, snakes throughout the entire sys-tem. In general. troubleshooting of cam-corder power circuits is accomplished inthe familiar manner of starting from apoint where the power is absent and mov-ing toward the power supply until youfind the point where it is present, or start-ing from the power supply and movingdown stream until it disappears.

Along the way, it helps if you can readthe route maps and signposts that themanufacturer has put there for you, suchas plug and connector numbers and cir-cuit designations. See the sidebar forsome notes on labeling of the intercon-nections among printed circuit boards.II


Servicing TV standby circuitsBy Homer L. Davidson

in order for remote -control TV sets to beable to be switched on using the remotecontrol transmitter, the remote controlreceiver at the set must be powered, evenwhen the set is turned off. The standbypower circuits provide voltage to thestandby circuits when the TV chassis isturned off. In other words, the standby cir-cuits are on all the time while the TV cir-cuits are off. Occasionally, these circuitsdevelop problems and must be serviced.Always use an isolation transformer whenservicing TV standby circuits (Figure 1).

When the TV "on" button on the remotecontrol transmitter is pressed, the voltagesupplied by the standby power supply ac-tivates the remote control receiver cir-cuits to enable the chassis to begin oper-ation. When none of the buttons on theremote unit will operate the TV chassis,suspect a defective remote control trans-mitter. Check the remote transmitter withthe IR (infrared) card or remote tester. Ifthe results of this test are inconclusive,substitute another remote to see if it willoperate the TV.

If the remote control transmitter ap-pears to be operating normally, suspectproblems within the TV standby circuits.If the set doesn't respond when you pressthe "on/off' button on the remote -controltransmitter, possible causes are a defec-tive standby power source, defective re-mote control circuits or a dead TV chas-sis. Determine if the TV chassis is deadby using the "on/off" button at the set, orby shunting around the standby circuits.

Standby or TV circuits?In older remote -control TV sets, the re-

mote -control transmitter actuated an acenergized relay to provide power -linevoltage to the TV chassis. You may finddc -operated relays in later standby cir-cuits. Other standby circuits, as in theRCA chopper power supply and Syl-vania's standby/full power supply enablethe switched mode power supply (SMPS)to activate the standby transistor circuitsfrom the chopper or switched mode pow-er transformer.

Davidson is a TV servicing consultant for ES&T.

Figure 1. Check over the TV chassis to locate the remote relay and control circuits. Always usean isolation transformer when servicing standby TV circuits.

In some cases, the standby circuits arenot included on the TV schematic. Youcan, however, easily spot the power relayof the standby circuits on the TV chassis.With the TV on the service bench, tracethe switch contact wires back to the powerline to determine which contacts must beshorted in order to bypass the relay. Ifthere are only two switched contacts onthe relay, clip a test lead across theswitched contacts to see if ac voltage isapplied to the TV chassis (Figure 2). Youknow that there are problems in the stand-by circuits if bypassing this relay bringsthe set to life.

Another method to determine if the TVchassis is alive is to take a power cordwith alligator clips, connect it across thebridge -rectifier diodes, and plug that cordinto the power line. Look for the degauss-ing coil and thermistor in the power -linecircuit. Make sure that the clips are oppo-site the common ground and B+ voltageterminals of bridge rectifiers. If the TVchassis still does not come on, the prob-lem is in the TV chassis, not the standbycircuits. Often the standby transformer ismounted off of chassis while the standbycircuits may be near or included in thetuning circuit board.

Transistor or relay circuits?In the latest RCA standby circuits, the

chopper transformer is on all the time, andthe secondary winding provides voltageto the standby circuits via the chopperoutput circuits. When the chopper outputtransistor is turned on by the regulator IC,current flows through the primary wind-ing, transferring energy to the secondarywinding of the transformer. This pulsat-ing voltage is rectified by a silicon diodeand supplies 15V source to the 5V stand-by regulator (Q4601). The 5V standbyvoltage is developed at the emitter termi-nal of Q4601.

In the case of another set, the Sylvania25/26B1 chassis, the standby power sup-ply is alive anytime the TV set is pluggedin. A standby power transformer suppliesvoltage to a transistor -operated dc relaycircuit (Figure 3). A 33V supply providesvoltage to the "on/off' relay. In additionto the 33V source, a 10.5Vdc source is fedto the 5V IC regulator (IC303), where the5V source voltage is developed for use bythe microcomputer, IC302.

The 5V source is applied to pin 28 ofIC302 and when the set is on, a low sig-nal at pin 1 will keep Q471 off allowingthe 10.5V source to forward bias Q472.


REMOTE SOLENOID RELAY

JUMOER

CLIP LEAD

Figure 2. With the TV chassis on the service bench, bypass the relay by clipping a test leadacross the relay contacts to determine if the TV chassis is functioning.

Relay K476 is energized through Q472when the transistor is forward biased.

A high signal from IC302 pin 1 will turnon Q471, taking the supply source toground, allowing Q472 to turn off. Withno voltage applied to the relay, the con-tacts open, removing ac voltage.

Turn -on methodsAnother way to force the chassis to op-

erate, besides clipping around the relaypoints, is to clip a wire from pin 1 of themicrocomputer, IC302, to ground (Figure4). The Sylvania C9 series chassis can beturned on by connecting across the collec-

tor and emitter terminals of the modeswitch transistor (Q410). The RCA CTC-168/169 chopper power circuits can beturned on by placing a jumper across thebuffer transistor (Q4306).

Standby circuit problemsProblems in the standby circuits may

be caused by dirty relay points or an openrelay solenoid coil. Clean up the switchcontacts with a thin piece of cardboardand cleaning fluid. Fine sandpaper maybe used to clean up tarnished silver con-tacts, but don't use emery, which is con-ductive. Forcing the switch contacts

closed using an insulated pen or a plasticrod, should cause the TV chassis to comeon, if the set is not defective. You mayhave to remove the top plastic cover ofthe relay in order to do this.

If you measure a voltage across thesolenoid coil, suspect that the coil is open.You may find both switching and coilwinding terminals on the relay. A quickcontinuity measurement with ohmmeteracross the coil terminals may indicate anopen winding. Check the standby voltagesource when a relay that checks good willnot energize.

The standby voltage source may be lowor absent causing the remote circuits tomalfunction. Leaky silicon diodes mayblow the main fuse or open the primarywinding of the standby transformer.Because the secondary winding consistsof heavy wire, if there is a heavy overloador if there are leaky components in thevoltage source or connecting circuits, theprimary winding, which is a lighter gaugewire, may open. Do not overlook a leakytransistor or microcomputer IC. Remem-ber, some standby circuits may performin cold or hot ground circuits.

Low dc voltage may result from tran-sistor and zener diode regulation. Often

1C302MICROCOMPUTER

26 A 5V FROM IC303"E STANDBY VOLTAGE 50J/10E

ON: OVDCOFF. 1 9VDC

SHUNT PIN I STANDBYTO GROUND TO - TRANSFORMER

TURN ON IV CHASSIS T471

120vAC

ode

10 K'.'

0471

0472

D471

C474220,.F

0474

ON: 1.5VDC22011

OFF. OVDC

15K11 2.7KI:

0473C04078

1000, F

0472

IC3035V REG

POWER OWOFFRELAY K476

ON 27VDCOFF 33VDC

C477too .F

47,.

STANDBY5V SOURCE

120VACTO MAIN

POWER SUPPLY

Figure 3. The standby remote circuits within the Sylvania 25/26B1 chassis look like this.


0410SWITCH MODE

OFF: OVON: 0.6V

SYLVANIA 25/26 81 CHASSISSHUNT PIN 1 AND 14 TO

GROUND TO START UP TV CHASSIS

OFF: 13VON: OV

FROM U3103

SHUNT COLLECTORTO EMITTER TERMINAL

SYLVANIA C9 CHASSIS

+15V

SHUNT COLLECTOR TOEMITTER WITH TEST CLIP

04306 BUFFER

Al%

RCA CTC168/169

04304ON/OFF SWITCH

Figure 4. Use one of these methods to start up the Sylvania and RCA chassis with a clip test lead.

zener diodes may overheat and becomeleaky. Regulator transistors may appearleaky or become open if the dc standbyvoltage is missing. Do not overlook a low -voltage dc source. Standby voltage testpoints may be found in some standby cir-cuits. Remember, low or missing stand-by voltage source will prevent the remotecircuits from operating.

Standby voltage sourceThe standby circuits may consist of a

voltage source with halfwave or fullwaverectification. The standby power trans-former provides stepped -down ac voltageto a halfwave or fullwave bridge circuit(Figure 5). Standby voltages may ener-gize a relay or provide regulated voltageto transistor, IC and microcomputer cir-

cuits. Often, the standby voltage is fairlylow, +5V to +12V, to microcomputer ortransistor turn on/off circuits. Relay dcvoltages may operate from 12V to 20V.Some standby circuits may operate froma 120Vdc to 150Vdc source in chopper orSMPS power circuits.

Silicon diode D101 rectifies the 14Vacvoltage to dc and operates relay RL1

AC INPUT

.011

FROMMICROCOMPUTER Ow

T101 D101 3900

101

0.01 ofD102

1.5K0

VVVNI

RL1POWERRELAY

0101RELAY DRIVE

330AFT0104

t2V SOURCE

Figure 5. A typical halfwave standby voltage source with standby power transformer and power relay.


when the microcomputer turns on therelay driver or switch transistor. C101 andR102 provide RC filtering in the 6Vsource. Zener diode D104 regulates the6V source. D102 provides 14V regulationwith 8101 (1200). The 14Vdc standbyvoltage source applies voltage across therelay solenoid winding with Q101 toground. Q101 acts as a turn -on switch orrelay driver when turned on by a micro-computer chip. When Q101 is turned on,the collector to emitter terminals form aswitch to ground, applying the returnvoltage to the standby relay.

General Electric 13BC-2 transformerIn a General Electric 13 -inch portable,

the remote control transmitter would notturn the TV on. I located the standby relayand clipped a jumper wire across the relaypoints. When the power cord was pluggedin, the TV sound and picture came up atonce. The remote problem was definite-ly in the standby circuits or in the remotetransmitter.

When the remote transmitter testednormal, I concluded that the trouble mustbe in the TV chassis. After locating thestandby transformer, I found the standbypower supply on the BC interface board.I measured the voltage at the main filtercapacitor C5 (1000µF). It was zero. Acheck of the schematic revealed that allvoltages of the tuner control came fromterminal strip PE247, supplied by the BCinterface board.

Silicon diodes YO1 and YO3 checkednormal according to the diode tester. Aquick test across the diodes showed that

P61-RL1

TO 14V - 16V

2

1-c SOURCE

STANDBY 0120VAC TRANSFORMER

3

4 TO RELAY0

OPEN PRIMARYWINDING

Figure 6. The remote control would not turn the TV on in a General Electric 1313C-2 portable.Diagnosis revealed that the primary winding of the standby transformer was open.

the ac voltage was zero. I shut the setdown and made a continuity check of thesecondary transformer windings at RL1on the interface board. They were good.When I measured the primary windingwith the ohmmeter, this winding wasopen (Figure 6). Replacing the standbytransformer solved the problem.

No 12V standby voltage:Sharp 13H44B portable

The remote control would not turn ona 13 -inch 13H44B Sharp color portableTV, so I pulled the chassis back to locatethe standby transformer and circuits.Power transformer T701 is mounted offof the PWB-F board containing the stand-by power voltage and tuning control cir-cuits. The primary winding contains pcwiring REI and RE2 and the secondary

winding ac voltage is found at RE4 andRE5 of the PWB-F board.

Voltage across the main filter capacitor(C1604), in the standby circuits, testedaround +20V (Figure 7). This dc voltagefeeds through R1601 to the collector ofthe 120V regulator transistor (Q1601).Voltage at the emitter terminal was zero,with higher than normal voltage at thecollector terminal. Diodes D1605 andZD I601 tested normal. Often, when aleaky or open voltage regulator is found,the base diodes appear leaky.

I tested Q1601 in -circuit with the diodejunction test of the DMM. It appeared tobe open. I tested the transistor once againafter removing it from the chassis. It wasdefective. I looked up the 2SC1983 reg-ulator in the semiconductor manual andfound that Q1601 could be replaced with

T701

120VAC

401

RE4

D1601 D1603 1E

C16031000F

RE5 01602 D1604

R1801

C1604

111

17.5V

0160112VREG

R1602

12V

OPEN

12.9V

D1805 1r

ZD160

T

+12V

C160433,F

CIRCLED OV(10._ MEASURED WHEN

01601 OPEN

Figure 7. The voltage regulator 01601 was found open in the standby 12V source in a Sharp 13H44B TV.


5V SOURCE mg

T401

SWITCHEDMODE

CIRCUIT

.geR43110it

D433

OPEN

L415

IC309

D431

FROMTUNER IIIII

CONTROL

R43747012

4D304

0430MODE SWITCH

R428122

0.7V

I C337Ts 330AF

0.03V

R44147022

0431STANDBY POWER

SWITCH

+1201/

123V

C4040.039,,F

1.1V

0432STANDBY POWER

SWITCH

123V

2.4V

+2.4V

1.1V

+2.41/

Figure 8. Extremely low voltage at the emittertransistor.

a SK3929 universal replacement. After Iinstalled the replacement transistor, the12V standby voltage source came up andthe set now operated normally.

Philco 200805: No remote actionThis 200805 Philco 20 -inch TV has a

standby and full -power circuits like thosefound in Sylvania's Switched -ModePower Supply (SMPS) circuits. When theset is plugged into the power receptaclethe SMPS begins running in the standbymode. This particular set remained inop-erative, no matter what button I pressedon the remote control transmitter.

I began my diagnosis by locating theswitch -mode transistor (Q410), standbypower switch (Q431), and standby powerswitch (Q432) in the front center of theTV chassis (Figure 8). I connected ajumper wire across the collector and emit -

terminal of 0431 was caused by open coil L415 in the 120V source of the standby power switch

ter terminal to turn on the TV set. Thechassis began to operate.

Voltages measured on Q431 were verydifferent from the specifications. Theemitter voltage should be rather high, butwas very low. I checked R438 ( 1 0) resis-tor and D433 and both were normal. Theac voltage on the anode of D433 was zero,as was the dc voltage at the cathode ter-minal. The cause of the problem was anopen coil, L415. L415 couples the ac volt-age to the silicon diode from the switchedmode power circuits.

No remote operation in anRCA CTC166

In an RCA CTC166 chassis the remotecontrol would not operate the set. The 5Vstandby source was very low. In anotherCTC166 chassis, the 5V source was miss

ing entirely. When the standby powersupply voltage is extremely low, look out-side the standby voltage sources to findthe overloaded component. The IE pre -amp IC (U3401) was found leaky in bothof these cases.

ConclusionWhen a TV set that has a remote con-

trol fails to respond to commands fromthe remote control transmitter, first checkthe standby voltage source for low ormissing voltage. Check the diodes, filtercapacitor, voltage regulator transistor andzener diodes in the standby voltagesource. Look outside the voltage source,when the voltage is extremely low to finda leaky component overloading the stand-by circuits. Locate the standby transform-er or relay connected to the standby remotecircuits when a schematic is not available.


Figure 1. Will the neon lamp in this circuit glow

The questions in this issue were tokenfrom previous TYEKs.

1. Which of the following is a measureof power?

A. ergsB. joulesC. joules per secondD. erg-seconds2

2. The period [T] of a certain pure sinewave is 0.001 second. Can you find thesecond harmonic of this waveform?

3. Regarding the circuit of Figure 1, theneon lamp will glow when the switch[SW] is

A. opened.B. closed.C. Neither choice is correct.

Wilson is the electronics theory consultant for ES&T.

Test Your ElectronicsKnowledgeTYEK revisited

How much do you remember fromprevious TYEKs?

By J.A. Sam Wilson

when the switch is opened or closed?

4. Everyone knows that a strain gaugemeasures strain. Or, does it? Do not con-fuse the terms stress and strain. Which ofthe following is correct?

A. Stress is the force that producesstrain.

B. Strain is the force that producesstress.

5. Is the following statement correct?The current gain of an emitter follower isless than one.

A. correctB. not correct.

6. What does the symbol in Figure 2stand for?

7. Which of the following electricmotors is likely to be damaged if it is oper-ated without a mechanical load?

Figure 2. What does this symbol stand for?

A. step motorB. shunt-wound motorC. series -wound motorD. capacitor start motorE. synchronous motor

8. Anything you do to increase the gainof an amplifier will automatically de-crease its

A. distortion.B. cost.C. phase shift.D. bandwidth.

9. The reciprocal of reactance isA. susceptance.B. conductance.C. elastance.D. impedance.

10. A certain analog meter is rated at100,0000 per volt. The amount of cur-rent required for full-scale deflection is

A. 100 microamperes.B. 50 microamperes.C. 25 microamperes.D. 10 microamperes.E. 1 microampere

(Answers on page 62)


ProductsEnvironmentally -safe spray

cleaner and preservativeIntroduced by Caig is an environmen-

tally -safe aerosol for its ProGold productline. ProGold's active ingredients are for-mulated to clean, lubricate and protectgold, base metals and other preciousmetal connector surfaces without theneed for carrier solvents for dilution orcleaning surfaces. The spray containerprovides short bursts of 100% concen-trate of the product via a precisionmetered valve.

The substance is a non-abrasive/non-corrosive formula that conditions goldconnectors, enhancing the conductivitycharacteristics to efficiently transmitelectrical signals. It coats the entire con-nector surface, providing protection fromabrasion (insertion resistance) and wear,arcing and RFI, tarnishing and atmos-pheric contamination. Pretreating withthe product will reduce intermittent con-nection problems, increase transmissionquality and product reliability accordingto the company.

The cleaner/preservative is for use onedge connectors, batteries, interconnect-ing cables, plugs, sockets, switches.relays, and other metal surfaces, etc.


DOS technical supportAn updated release of TechSource for

DOS, a hyper -text database resource pub-lished using the Folio Views engine, hasbeen announced by Ontrack ComputerSystems. Designed for use by technicalsupport and computer service techni-cians, the software provides informationabout hardware, software, product histo-ries, field reports, and operating sys-tems-both current and out-of-date ver-sions-and more. The product nowincludes Disk -Source, a hard disk driveand controller encyclopedia, and System

Source, a reference to computer systemboards including jumper settings andBIOS information.

This product provides information forpeople working in DOS, Novell, Unix,and Macintosh environments. Functionsinclude product history, as well as hard-ware, software, and operating systeminformation. Hardware informationincludes various jumper settings, andhardware and software interactions.Software information includes features,limitations, configuration details, andhardware and software interactions.

DiskSource, which is also available asa separate product, contains technicalspecifications on more than 3,000 harddisks, with drive jumper settings on over1,200 disk drives and 400 controllercards, plus more than 60 BIOS charts.

SystemSource, available as a separateproduct, is a comprehensive collection oftechnical information on more than 500system boards from more than 35 differ-ent manufacturers.


Power monitorBMI's new 120 PowerSpy power mon-

itor detects wiring errors and all powerdisturbances on line -to -neutral and neu-tral -to -ground voltage. Users plug theirsensitive load into the unit's stackingplug, then into the outlet. Front panelLEDs light to indicate power distur-bances and diagnosis.

Hm0120 PowerSpy- Power MonitoLI no-lohloanrI - - INIulri.lo-Groung -

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If a power disturbance occurs, a latch-ing red LED lights and stays lit until theuser presses reset. At the same time, theappropriate diagnosis LED also latcheson, indicating suggested actions, such asinstalling power conditioning. If powerfails, the monitor stores LED settings for48 hours.

The product detects wiring errors, sags,swells, impulses, waveshape faults, high -frequency noise, and power failures.


Isolation transformerShape Electronics has announced the

availability of Sentrex isolation trans-formers, offering protection of electricalequipment from the harmful effects ofnoise, spikes and surges on power lines.The transformers are lightweight, com-pact and virtually silent.

Isolation transformers may be used inany application that is vulnerable to dam-age from electrical noise on power lines,Including factory automation equipment,mini -computers, automated teller ma-chines, laboratory equipment and homeentertainment systems. The transformersare especially well -suited for generator -powered applications since they are notaffected by frequency fluctuations, andloads with high inrush current such aslaser printers, copiers and motors.

This device acts as a barrier, isolatingequipment from the contaminants of thepower utility, such as spikes and surges.This "isolation" reduces the electrical

(Continued on page 41)


Products (from page 28)

noise and virtually eliminates the noiseon the ground, stopping "ground loop"currents and improving the overall oper-ation and reliability of the equipmentbeing protected. A built-in solid-stateMOV device offers additional electricalsurge suppression.


Modular test lead kitsThe 9100 series kits from Probe Master

are available with up to 25 different mod-ular plug-in accessories, such as sprunghooks, pincer hooks, wire piercing hooks,

extender probes, alligator clips, and five -way telephone clips. The leads aredesigned for long term reliability withflexible strain relief, 440 strands of wireand silicone insulation. They are softeryet impervious to hot soldering ironburns. Kits are offered with straightretractable shrouded banana plugs orright angle fixed shrouded banana plugs.


Air -power spray bottle replacesconventional aerosols

Tech Spray, Inc. has introduced TheSpritzer, a new air -power spray bottle thatprovides an environmentally consciousalternative to conventional aerosols.

The refillable, reusable spray bottleuses only compressed air as a propellant.After filling The Spritzer with liquid andreplacing the lid, a simple pump built intothe base of the polypropylene bottle isused to pressurize the unit.

In addition to the environmental advan-tage, customers can save money by buy-

ing liquid solvents in bulk. The durableunit will replace the use of more than 500aerosol cans.

The Spritzer uses no harmful chemicalpropellants and its use has the potentialof reducing waste. The dispenser alsocomplies with EPA recommendations for"not -in -kind" cleaning alternatives.


Time Motion ToolsQuality Field Service Tools and Tool Kits for the

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Circle (91) on Reply CardMay 1994 Electronic Servicing & Technology 41

* * * SHOWCASE OF TOOLS & TOOLCASES * * *Every type of work requires a set of

tools. The artist, the craftsperson, thetechnician, the mechanic; each pro-fession needs an assortment of toolsthat is specifically designed to assistin getting the job done thoroughly, effi-ciently, neatly.

The consumer electronics servicetechnician requires an extensive andvaried assortment of tools to performthe operations required to gainaccess to the operating componentsof the product being serviced.

To begin with, the technician mayneed some screwdrivers, nutdrivers,wrenches, pliers, etc., simply to getthe back or cover off of the product.

Once inside the product, the tech-nician may still need the same tools,along with some additional tools, todisassemble the chassis further togain access to test points and sus-pected portions of the circuitry.

Once the technician has diagnosedthe problems, he will need tools suchas IC pullers, soldering/desolderingtools, common hand tools, etc., toremove the failed component(s) ormodule(s) and to install the replace-ment parts.

Many of the common hand toolscan be used in servicing a broad vari-ety of consumer electronics products,but many specific products requirespecific tools in order that servicingmay be completed quickly by the tech-nician and efficiently.

For TV work, for example, the list ofspecial tools may include an assort-ment of nonferrous alignment tools.The tape transport of a VCR requiresseveral specialized tools for adjust-ment. If you're going to be servicingpersonal computers, you'll probablywant to have IC insertion and extrac-tion tools, Torx fastener drivers, anda keycap puller for the keyboard.

Depending upon what specificproducts you'll be servicing, you mayneed, or wish you had, specializedsoldering/desoldering tools and tips.

Tool kits/casesWhen it comes to assembling a tool

case so that you can get as much workdone on site as you possibly can, the

problem of selecting tools becomeseven more critical than the selectionof tools for the service center. Youwant to have every tool on hand thatyou might possibly need, but not a sin-gle tool that you'll never use. After all,there's no point in lugging aroundexcess weight. You want every tool inits place so you don't forget anythingwhen you go out to make the call, andespecially when you leave the site.You want your toolcase to be light-weight, but rugged.

Assembling a set of toolsSo how do you decide what you'll

need in the way of tools, and how doyou find out about those useful spe-cial tools without which you mighthave more difficulty getting the jobdone, or possibly even damage thevery product that you're trying torestore to operation?

A very good way to determine whattools you'll need to get a particularproduct serviced is to study the ser-vice manual for that product, if you canobtain one. Usually good service lit-erature provides a list of special toolsthat the service technician will needto complete service on the product.

Another way to assemble the arrayof tools you'll need is to consult witha colleague who is already servicingsimilar products.

One of the best ways to be sure thatyou have the right tool at hand is toconsult an established, reputablevendor of tools and/or tool cases.These companies deal with servicetechnicians and service managersevery day, and in most cases offer akit of tools, or several variations, foreach specific type of service.

Thus, if you plan to service person-al computers, for example, thesecompanies will have available sever-al tool kit selections, depending howdeeply you want to get into it, and howextensive your tool selection isalready. The same is true for copierservice, telecommunications service,or service of other products.

Check out the showcaseA number of tool and tool case ven-

dors are featured in this issue. Thespace that they have been given inaddition to their ads has allowed themto tell readers a little about them-selves and the products and servicesthey offer.

If you're in the market for tools,toolkits or toolcases to expand the lineof products you'll be servicing, shoparound in our showcase and see if youfind what you're looking for. If youdon't see it, ask: that is, check theappropriate number on the readerservice card.


* * * SHOWCASE OF TOOLS & TOOLCASES * * *

RS Electronics34443 SchoolcraftLivonia, MI 48150Phone: 313-525-1155800-366-7750Fax: 313-525-1184

Founded in 1929, RS Electronicsranks as one of the top electronics dis-tributors in the U.S. We offer electron-ic components and test equipmentfrom more than 200 manufacturers.Our company constantly strives toachieve a high quality of service in sup-plying products to a wide variety ofmaintenance and service organiza-tions-from small independent servicecenters to the service divisions ofAmerica's largest companies. Wehave compiled an enviable record.

In spite of this success, RS has notforgotten that companies that maintainand service electronics equipmentcan't always buy their supplies in largequantities. At RS, you can buy whatyou need at reasonable prices, even ifyou only need a few items.

Our product lineThe RS Electronics product line

includes oscilloscopes, DMM's andtest probes from Tektronix, Fluke, B&Kand Leader; diagnostic circuit testersfrom Huntron; soldering and desolder-

ing tools from Weller, Ungar and OKIndustries; chemicals and cleaningsupplies from Techspray; hand toolsfrom Diamond, Ungar, Utica, Wire -Wrap and Xcelite; fuses, circuit break-ers, wire and heat shrink tubing,switches and resistors; all in stock andavailable for immediate delivery.

To maintain our high standards ofservice and our high standing with ourcustomers, we work tirelessly to iden-tify customer needs and to respondwith effective solutions. Flexibility andcreativity are the hallmarks of RSElectronics.

RS Electronics offers a broad rangeof services that is unique in the indus-try, from simple off -the -shelf ship-ments to full strategic partnerships.

At a time when many distribjtors arereducing their product lines as aneconomy measure, RS Electronics is,in contrast, continuing to expand itsproduct line in order to meet the needsof customers. We supply millions ofcomponents from over 200 productlines. RS maintains substantial inven-

tories at our three regional warehous-es, available for immediate delivery.We are a broad line distributor withdepth and breadth of product in ALLmajor categories.

The RS Electronics line of toolsand tool cases

Our line of tools and cases includes: Cooper Tools

BonneyDiamondEremUngarUticaXcelite

GC Thorsen Greenlee Tools Ideal Leviton 3M Paladin Platt

Convenient locationsWith fully -stocked branch offices in

ten cities in the U.S. (see advertise-ment on the inside back cover for loca-tions) open from 8 a.m. to 5 p.m., RSElectronics is able to deliver ordersquickly and accurately. Our dedicatedFax order lines are operational 24hours a day, seven days a week, 365days a year. If your order is placedbefore 4 p.m., in more than 99% ofcases we are able to ship stock itemsthe same day.

Have a look at our catalogTo receive a copy of the latest RS

Electronics catalog to see the manyways in which we can fill your elec-tronic products needs, contact yourclosest RS branch office, or check theappropriate number on the ReaderService card in this issue.



Tentel4475 Golden Foothill Pky.El Dorado Hills, CA 95762Phone: 916-939-4005800-538-6894Fax: 916-939-4114

A VCR contains rubber belts, wheels,idlers, gears, brakes and tension bandsthat are there to maintain the propertorques and tape tensions during the var-ious loading, play, rewind, fast forward,and stop modes. All of these, plus theactual video head tips are subject to nor-mal wear.

Every time the consumer plays a tape,these components stretch, wear, shiftposition, and are stressed. Contaminantsand oxygen, in the air, cause many ofthese parts to age and break down evenwithout use.

By the time a VCR requires service,several of these components are proba-bly out of tolerance. Nine out of ten (90%)VCRs brought in for service have

rather than electronic, prob-

lems. When a customer brings in a VCRfor service, the entire tape transport sys-tem should be checked.

Since many components in the trans-port are subject to wear during its use,once the immediate cause of the problemhas been corrected, you should performa thorough check of the other mechanicalcomponents to be sure that they too arein proper operating condition.

If you merely correct the immediateproblem and return the VCR to its ownerwithout a thorough check, there's anincreasing risk that one or more mechan-ical components will soon either fail orcause erratic operation. The result of allthis is a disgruntled and possibly lost cus-tomer, and either a callback that wastestime or, even worse, the customer tossesthe VCR in his closet and purchases a newone, carefully selecting a different VCRmanufacturer. (It's the same for cars, ifyou get a "lemon" and the dealer can't fixit properly, the customer will typicallychange to a different manufacturer)!

That's why every VCR service shouldinclude a check, and adjustment if nec-essary, of tape guide heights, holdbacktape tension, and numerous torques(including FF, REW, brakes and restoringtorques). All of these checks and adjust-

ments are specified in the service manu-als of every manufacturer. You may alsofind it valuable to check the video headwear to see how many more hours of lifethe VCR owner can expect from them.

With the proper tools: torque, back ten-sion gauge, reference plane, head pro-trusion gauge, etc., all of the tests andadjustments can be performed in just afew minutes.

A thorough test and adjustment willallow the service center to do it right thefirst time, and possibly collect a little moremoney for performing all the work thatshould be done anyway, plus you'll avoiddisappointing the customer and avoidthose dreaded callbacks.

And how much does it cost for all therequired mechanical test tools? More thanor less than other necessary test equip-ment, such as a good scope? Actuallymuch less than! $1100 to $1700 will buyall of the mechanical test tools you needto perform all of the mechanical tests andadjustments shown in factory servicemanuals. The time you save in servicingVCRs more efficiently, performing higherquality repairs, and in avoiding the highcost of callbacks will easily pay for theseproducts; providing the best VCR repairvalue for their hard-earned money.

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Circle (73) on Reply CardMay 1994 Electronic Servicing & Technology 47

BooksThe Illustrated Dictionary of Elec-

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American Megatrends, Inc., manufac-turers of AMIBIOS, has now created acomprehensive programmer's guide ofinformation on this software. This guidenot only describes all standard ISA andEISA system BIOS functions, butincludes complete documentation of thenew PCMCIA Socket Services, Ad-vanced Power Management (APM), andPeripheral Component Interconnect(PCI) BIOS functions.

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What Do You Know About Electronics?

More about capacitor timeconstants and the GROLBy J.A. Sam Wilson

I have always said that the good part ofteaching was the exchanges I had with thebest students. They have taught me much.When I got careless they let me know, andwhen I presented them with valuable in-formation they let me know about that too.I miss that exchange, but I do get muchof the same thing by writing this column.

A good example is the letter I got thisweek from Phillip J. Andres IV who makesWheaton, IL his home. Here is his letter:

Dear Mr. Wilson,1 have always enjoyed your quizes and

columns, but today 1 have to speak outabout your hidden puzzle on page 55 ofthe December '93 ES&T

Of course, we all know that when cur

Wilson is the electronics theory consultant for ES&T.Figure 1. This time constant circuit permits the capacitor to be charged or discharged, depend-ing on the position of the multi -position switch.

w

100-

90-

80-

(0, 100) 0 (5, 100)

1

LEGENDS(CHARGING)

470- 1, 63.2

2,oti (1, 63.2) 3,60- 4,

5, 100U.u.0

50-DISCHARGING

cc 40 1, 36.8O'

30 -

(1, 36.8) 2,3,4,5, 0

20-

10-(0, 0) (5, 0)

°T1 2 3

TIME CONSTANTS

T54

Figure 2. You can use this system of coordinate axes to plot the charge or discharge of ar RC circuit.


TABLE 1Step 1: Voltage of the previous step:Step 2: Subtract the voltage in Step 1 from 100:Step 3: Multiply the voltage in Step 2 by 0.632:

VVV

Step 4: Add the voltage in Step 3 to the voltage in Step 1: V

Step 5: Enter the value on the graph and in legend for a charging capacitor

Example-

To plot the point on the second time constant line after the point on the first timeconstant line has been plotted:

TABLE 1Step 1: Voltage of the previous step: 63.2VStep 2: Subtract the voltage in Step 1 from 100: 36.8VStep 3: Multiply the voltage in Step 2 by 0.632: 23.3VStep 4: Add the voltage in Step 3 to the voltage in Step 1: 86.5VStep 5: Enter the value on the graph and in legend for a charging capacitor

Table 1. This is a step-by-step procedure to find the time -constant points on the RC charginggraph.

100

90

80 -

(0. 100) (5. 100

LEGENDS(CHARGING1

70 ---

60 - (1, 63.2)1, 63.22, 86.53, 954. 98

50 5, 100

40 DISCHARGING

(1, 36.8)1. 36.8

30

20

2,3,4,5, 0

10

(0, 0) (5. 0)0

I I

1 2 3 4 5

TIME CONSTANTS

Figure 3. Connecting the points that you have plotted on the charging time -constant coordinateaxes with straight lines gives this piecewise curve.

rent flows in the same direction in paral-lel conductors, the conductors will be at-tracted to each other, not repelled. It wasthe attraction of the strands to each otherwhich reduced the flexibility. The effectwould occur without the sheath.

Just wanted you to know I was payingattention.

Phil Andres

Many thanks for your letter Phil (and,to everyone else who caught that error butforgot to write to me about it)!

You are absolutely right! I was in ahurry and put down something I thoughtI knew without checking.

Historically, this fact came up whenMr. Ampere set out to define current mea-surement. He used the attraction or repul-

sion between two parallel wires carryingcurrent to define an amount of current.Later, the unit of current was named theAmpere in his honor.

So much for writing things I thought Iremembered, I'll look it up next time.

I still say there is an invention lurkingin that subject-something that hasn'tbeen done before.

Confucius Says (or, people says Confu-cius says): He who makes too many mis-takes does nothing, but, he who makes nomistakes also does nothing.

A piecewise approach to GROLtime -constant problems

The GROL exam is the new FCC examthat is used to replace the previous firstand second class licenses. GROL standsfor General Radio Operator License.

So far, we have looked at the solutionof time constant problems using a math-ematical approach and a graphical ap-proach. Now we will extend the graphi-cal approach so that you don't need auniversal time constant curve. Part of themethod in this issue makes it possible toeasily solve all of the time constant prob-lems in the FCC GROL exam.

The graphical method of solving timeconstant problems discussed previouslyrequired a universal time constant curveas a starting point. But, what to do if youcan't lay your hands on a universal timeconstant curve?

The answer is that you can construct thecurves by using some very easy calcula-tions. It is easier if you have a calculatorthat can handle addition, subtraction,multiplication, and division.

The time constant circuit of Figure 1permits the capacitor to be charged or dis-charged. Both curves will be developed.

Refer to Figure 2. It is the coordinatepair that you will use to plot a piecewisetime constant curve. The horizontal axisis used for time constants and the verticalaxis represents the applied voltage, or thepercent value of the applied dc voltage.For convenience we can say the verticalaxis is marked for 100V. However, it canalso represent 100% of any voltage.

Start the simple graphical procedure byconstructing coordinates shown in Figure2. It doesn't make any difference whatspace you use for the marks as long asthey are evenly spaced on the two coor-dinates. There is no relationship between


100

90 -

80-

70

60

50-

40 -

30 -

20 -

10 -

(0, 100)

(1, 63.2)

(1, 36.8)

2

TIME CONSTANTS

4

(5, 100)

LEGENDS(CHARGING)

1, 63.22, 86.53, 954, 985, 100

DISCHARGING

1, 36.82, 13.53, 54, 25, 0

5

(5, 0)

Figure 4. The complete charging/discharging curves for the RC time -constant circuit of Figure 1 look like this.

the sizes of vertical and horizontal spaces.You know that at the start of the charg-

ing cycle (T = 0) the voltage across thecapacitor is OV. That point (0,0) has beenmarked on the graph (Figure 2).

Remember that the capacitor is notcharged at the start. When the switch isturned to potition 'B' capacitor (C) beginsto charge through resistor 'R'. It has beenshown that at the end of one time constantthe voltage across the charging capacitorwill be 63.2% of the applied voltage. Thatis the same as 63.2V on our graph. That

point (1,63.2) has been marked on Figure 2.For practical applications the capacitor

is considered to be fully charged at fivetime constants. So, (5,100) has beenmarked on the graph.

At the start of the discharge period thevoltage across the capacitor is consideredto be 100V. Point (0,100) has been markedon the graph.

It has been shown that voltage acrossthe discharging capacitor will drop to36.8% of the original full -charge voltagein one time constant. That point, (1,36.8)

TimeConstant

Value

TABLE 2Time Time

ConstantValue

ConstantValue

Time TimeConstant Constant

Value Value1

Charging2 3 4 5

Voltage, or 63.2% of fullvoltage

Discharging

86.5 95 98 100

Voltage. or 36.8% of full

13.5 5 2 0

Table 2. Performing all of the calculations for the first five time constants for chargingdischarging of the RC time constant circuit of Figure 1 yields these data.

and

is marked on the graph of Figure 2.At the end of five time constants the

voltage (for practical purposes) hasdropped to OV. The point (5,0) has beenmarked on the graph.

So far there have been six pointsmarked on the coordinates in Figure 2.

We now continue with the constructionof the charging time -constant curve. Atone time constant the voltage across thecapacitor is 63.2V. Subtract that from 100and you get 36.8V. That is the remainingvoltage at one time constant. The capac-itor will charge 63.2% of that remainingvoltage during the next interval: 0.632 x36.8V = 23.3V.

That is how many volts the capacitorwill charge during the period between thefirst and second time constant. Then addthat voltage to the 63.2V at the first timeconstant:

63.2V + 23.3V = 86.5V

So, at the second time constant the volt-age across the capacitor is 86.5V. Markthat value on the graph and enter it intothe legend shown on the graph.

In order to simplify the problem of find-ing the points on the charging graph, a step-by-step procedure is given in Table I.


Continue to determine the remaining timeconstant values. Enter the values on thecoordinates of Figure 2 and in the legend.

Connect the dots on the graph withstraight lines. That gives you the piece -wise -charging time -constant curve. Atthis point, your graph looks like the onein Figure 3 and the complete data is shownin the legend.

Making the discharge curveWhen the switch in Figure 1 is turned

to position C, the capacitor dischargesthrough the resistor.

To mark the points on the graph for thepiecewise discharge curve all you have todo is subtract the point marked on thegraph for the charge curve from 100. Thatgives you the point for each time constant.

For example, the point marked for thefirst time constant is 63.2V. Subtract thatvalue from the full voltage of 100V andyou get 36.8V. Mark that point on the firsttime constant line. It is the first point onthe discharge curve.

For the second time constant line notethat the point on the charging curve is86.5V. Subtract that voltage from 100Vand you get 13.5V. That voltage has beenmarked on the discharging time constantline and also entered into the legend ofFigure 4.

Continue that procedure and mark the

voltage on each time constant line untilyou have marked the five lines.

Connect the dots with straight lines andyou have the piecewise time constantcurve for the discharging capacitor. Yourgraph now looks like the one in Figure 4.Be sure to complete the data in the leg-end as shown in Figure 4.

If you are one of those lucky peoplewith a flair for drawing you can add cur-vature between the dots on the graph. Thatwill bring you closer to the actual timeconstant curve.

By choosing 100V as the supply volt-age, the graphs we have made can bemarked in percent along the left edge. So,the 63.2V mark is at 63.2% of the maxi-mum supply voltage, the 86.5V mark isat the 86.5% mark, etc.

Solving FCC time -constant(GROL) problems

Now direct your attention to Table 2. Itis a compilation of all data in the legend.It gives the percent of full voltage for eachtime constant.

So what? Every time constant problemin the GROL exam is for the voltage atsome exact value of time constant asshown in the table.

If you followed the instructions for get-ting the points in the legends you cananswer any time constant problem in the

GROL exam! Here are three questionsand their solutions. The questions arecopied word-for-word from the pool ofquestions used by the FCC.

1. After two time constants, the capac-itor in an RC circuit is charged to whatpercentage of the power supply voltage?

Answer-From Table 2 the answer is86.5%.

2. What is the time constant of a circuithaving a 100µF capacitor in series with a470k0 resistor?

Answer-You don't need the table forthis one, but, you do need to be able tocalculate time constants to solve some ofthe problems in the GROL exam.

T = RC = 470 x 103x 100x 10-6 = 47seconds.

3. How long does it take for an initialcharge of 800Vdc to decrease to 294Vdcin a 450pF capacitor when a IMO resis-tor is connected across it?

Answer-First, find the time for onetime constant.

T = RC = 1 x 106 x 450 x 10-6=450 seconds.

Note that 294/800 = 0.3675 = 36.8%.That is the value for the first time constanton the discharge curve. Therefore, the ca-pacitor will discharge from 800V to 294Vin one time constant, or, 450 seconds.

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Video Corner

Understanding the CRT numbering systemBy The ES&T StaffBased on Sencore Tech Tip 145

It's not absolutely essential to be famil-iar with component numbering systems,but it can help reduce errors in orderingof a replacement part. This brief articleexplains the numbering systems on CRTsboth before and since the introduction ofthe Worldwide Type Designation System(WTDS).

Most CRTs are registered according tosome kind of industry standard. Thesestandards define certain characteristics ofthe tube. Since April 1, 1982, these stan-dards have been combined into a singleworldwide standard. Before that date, sev-eral non -universal standards were used.

Old standardsCRTs manufactured before April 1,

1982 were registered differently in theUnited States, Japan and Europe. In gen-eral, the registration number broke downinto three parts.

The first part of the old -type CRT num-ber is a series of digits which signify theminimum diagonal viewing measure ofthe CRT. For American tubes, this size isin inches. Thus a 19VACP22 would havea viewing diagonal measure of 19 inch-es. Japanese tubes have this distance inmillimeters.

The next part of the CRT number con-sists of one to four letters which designatea particular CRT within a group of CRTshaving the same screen size. The final partof the CRT designation indicates the typeof phosphor used. Black and white videoCRTs use a P4 designation for Americanlistings or a B4 listing for Japanese list-ings, while color CRTs use a P22 (Amer-ican) or B22 (Japanese) listing. ComputerCRTs or scope CRTs may use some othertype of phosphor, and will have a differ-ent number following the "P" or "B." But,as you see, the "P" or "B" is not part ofthe tube designation.

Some CRTs have listings that do nothave a "P" or "B" ending. The most com-mon non-standard ending is "TCOI" orTCO2." These CRTs always have bondedyokes (or some other component) perma-nently attached to the CRT neck. The"TC__" ending simply indicates the typeof yoke plug the CRT uses to connect tothe chassis. The CRT is identical to one

19 VAC P22

/1\diagonal CRT type phosphor type

Figure 1. Before April 1 1982, the numberused to identify picture tubes was different inthe United States, Europe and Japan. Here isthe number from an American CRT from thatvintage. The first two digits identifies the diag-onal picture size, the second set of charactersdesignates the CRT type and the third set ofcharacters designates the phosphor type.

with a "P22" or "B22" ending. For exam-ple, a 15VAETC01 is identical to a15VAEP22.

WTDS standardSince April 1, 1982, a new system for

categorizing and numbering CRTs hasbeen in use. This system is officiallycalled Worldwide Type Designation Sys-tem (WTDS) for picture tubes and mon-itor tubes. Until the adoption of this sys-tem, American, Japanese and Europeantube manufacturers had all numberedtheir tubes differently. This led to confu-sion and incomplete or inaccurate infor-mation. The WTDS number was an effortto simplify and unify CRT designations.

The WTDS number consists of sixgroups of symbols. The first symbol de-fines the application of the tube. This

symbol is always a single letter; either anA for picture tubes or an M for video mon-itor tubes. A second group of symbols isa two -digit number that defines the min-imum diagonal view. This measurementis always listed in centimeters (1 inch =2.54 centimeters).

The next group of symbols consists ofthree letters that designate a family codefor the CRT. Tubes within a particularfamily have specific mechanical and elec-trical characteristics. These letters are as-signed alphabetically beginning withAAA followed by AAB, AAC, etc.

One or two digits follow the familycode. These digits indicate a specificmember within a particular family. A dif-ferent member number would be assignedto tubes within the same family that havedifferent neck diameters, for example. Asingle digit member symbol indicates amonochrome tube while a two -digit num-ber indicates a color tube.

Following the one or two digit membersymbol is the phosphor type designation.Color picture tubes are designated by thesingle letter X, while color monitor tubesmay have some other single letter desig-nation. Monochrome picture tubes aredesignated by the two letters WW. Othermonochrome tubes, such as video moni-tors, have a different specific two -lettercode to designate the phosphor type.

Some tubes contain integral neck com-ponents, such as bonded yokes. Thesetubes have a sixth group of symbols as-signed to them. A two -digit number isused to define the characteristics of theseintegral neck components.

A

Application(picture)

62

Diagonal(in CM)

A62AAA0OX

AAA

Family00

MemberX

Phosphor(color)

Figure 2. When the Worldwide Type Designation System (WTDS) was introduced in April of1982, CRTs from all over the world were identified with the same six groups of symbols. One ofthe changes for U.S. manufacturers is that the diagonal size was now expressed in millimeters.


Computer Corner

A local bus primerBy John Kull

Throughout the history of the personalcomputer, hardware and software haveplayed catch up with the advancing mi-croprocessor technology. Computer busspeed has been one area in need of en-hancement. A new technology called "lo-cal bus" is probably the most excitingupgrade to come along in the computerindustry in a long time.

For the Windows or graphics basedprogram user, local bus can mean fasterscreen drawing and data transfer than waspreviously possible. If you are not famil-iar with local bus technology, this articlewill provide some background informa-tion on current computer bus technologyand explain what local bus technology isand what it can offer in terms of increasedperformance.

The expansion bus

The expansion bus provides the path-way to system memory, control and pow-er. The original IBM PC used an 8 -bit databus and a 20 -bit address bus that ran atthe system clock speed of 4.77MHz. Con-nection to the bus was made via a 62 -pin,0.1 -inch edge card connector (Table 1).As the PC evolved, the AT class was intro-duced. It contained an 80286 micropro-cessor with a 16 -bit data bus and a 24 -bitaddress bus that operated at a clock speedof 6MHz (Table 2). The larger address anddata buses required an additional 36 -pinconnector that mounted behind the exist-ing 62 -pin connector (Figure 1).

With the introduction of the 80386 mi-croprocessor, the clock speeds increasedfrom 8MHz to 16MHz and the data andaddress buses increased to 32 bits. It be-came obvious that the bus standard wasin need of an overhaul. At this point in PChistory, IBM and the compatible industrychose separate paths in their developmentof a new bus standard.

IBM developed a new protocol that wasincompatible with the original standard ithad developed. The new technology was

Kull is a medical electronics technician at the St. LouisRegional Medical Center.

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Figure 1. Eight -bit connector and sixteen -bit extension connector.

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Figure 2. The Micro Channel Architecture of the IBM computers features this new style edgeconnector with 0.05 -inch pin spacing.

called MCA, or Micro Channel Architec-ture. It used a new style edge card connec-tor with a 0.05 -inch pin spacing (Figure2). The design specification of MCAallowed bus speeds as high as 33MHz.

The EISA bus

The compatible industry decided tomake their new standard compatible withthe existing technology. The old standarddeveloped by IBM was then referred to

as ISA, for Industry Standard Architec-ture and the new technology was called"EISA," for Enhanced Industry StandardArchitecture. EISA used a double -heightconnector with two rows of contacts. Thetop row was for ISA signals and the bot-tom row carried the EISA signals. AnEISA card was designed to slip past thetop row of connectors and access the bot-tom row.

EISA provided access to the 32 -bit ad -


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8 ItIT ISA BUS CONNECTIONSl'in Number I/OAIA2A3A4A5A6A7A8A9A10AllAl2A13A14A15A16A17A18AI9A20\21\22

A23A24A25A26A27A28A29A30A31

B1B2B3B4135

B6B7B8B9BIOBIIB12B13B14B15B16B17B18B19B20B2IB22B23B24B25B26B27B28B29B30B3I

I/0vo1/0I/OI/0I/OI/O

0

00I/OI/O01

0

0I/O

1

1

1

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TABLE I

SignalI/O CHKSD7SD6SD5SD4SD3SD2SDISDO

I/O CHRDYAENSA19SAI8SA17SA16SA15SA 14SA 13SA 12SA I I

SA 10

SA9SA8SA7SA6SA5SA4SA3SA2SAISAO

GNDRESET+5VIRQ2/9+5VDRQ2-12VOWS+12VGNDSMEMWSMEMRIOWIORDACK3DRQ3DACK IDRQ IDACKOCLKIRQ7IRQ6IRQSIRQ4IRQ3DACK2T/CALE+5VOSCGND

Signal DescriptionI/O CHANNEL CHECKDATA BIT 7DATA BIT 6DATA BIT 5DATA BIT 4DATA BIT 3DATA BIT 2DATA BIT IDATA BIT 0I/O CHANNEL READYADDRESS ENABLEADDRESS BIT 19ADDRESS BIT 18ADDRESS BIT 17ADDRESS BIT 16ADDRESS BIT 15ADDRESS BIT 14ADDRESS BIT 13ADDRESS BIT 12ADDRESS BIT I I

ADDRESS BIT 10ADDRESS BIT 9ADDRESS BIT 8ADDRESS BIT 7ADDRESS BIT 6ADDRESS BIT 5ADDRESS BIT 4ADDRESS BIT 3ADDRESS BIT 2ADDRESS BIT IADDRESS BIT 0

GROUNDSET DRIVER+ 5 VOLTSINTERRUPT REQUEST 2/9+5 VOLTSDATA REQUEST 2-12 VOLTSCARD SELECT (XT ONLY)+ 12 VOLTSGROUNDMEMORY WRITEMEMORY READI/O WRITEI/O READDMA ACKNOWLEDGE 3DMA REQUEST 3DMA ACKNOWLEDGE IDMA REQUEST IDMA ACKNOWLEDGE 0CLOCKINTERRUPT REQUEST 7INTERRUPT REQUEST 6INTERRUPT REQUESTSINTERRUPT REQUEST 4INTERRUPT REQUEST 3DMA ACKNOWLEDGE 2TERMINAL COUNTADDRESS LATCH ENABLE+ 5 VOLTSOSCILLATORGROUND

Table 1. Eight -bit ISA connections.

dress and data path. (EISA met with verylimited success. Most users found the ISAbus provided them with sufficient perfor-mance). EISA and MCA both provided

32 -bit access but both were limited to an8MHz or 10MHz speed limit.

The main reason for the 8MHz speedlimit is compatibility. Most expansion


cards were designed to run at 8MHz. The8MHz speed limit allowed the faster mi-croprocessors to be compatible with theolder hardware. However this creates adata bottleneck. Data races between themicroprocessor and memory at the sys-tem clock speed on a 32 -bit data bus, butencounters a "bottleneck" at the 8MHz,I6 -bit expansion bus. To slow down themicroprocessor, "wait states" are added.

A wait state is a system clock cycle dur-ing which the microprocessor "waits" forthe device with which it is communicat-ing. Wait states are also used in faster mi-croprocessors to communicate withslower memory chips. Many mother-boards contain hardware jumpers or soft-ware settings to determine memory waitstates. The net result is a slowdown in sys-tem performance.

The local busLocal bus motherboards provide access

to the processor's 32 -bit address and data

buses via special local bus slots on themotherboard. An additional 124 pin, 0.05 -inch socket is mounted in line with the ISAconnectors and provides access to the lo-cal bus (Figure 3). This allows for directdata transfer to the microprocessor andeliminates the data bottleneck.

The bus specifications allow for speedsup to 66MHz and transfers data via a 32 -bit data path. Compared to the ISA bus,which operates at 8MHz and transfersdata via a 16 -bit data path, the local buscan exchange data up to six times as fast.As with all good things in life, the localbus does have a catch.

A special expansion card is neededfor each device

To take advantage of the local bus tech-nology a special expansion card is need-ed for each device that will access the bus.Currently, expansion cards are availablefor video, hard drive and network control-lers. At first, most local bus systems wereproprietary and required the user to pur-chase all expansion cards from the origi-nal manufacturer. Some vendors still in-corporate the local bus video into themotherboard. Most offer two expansionslots for access to the bus. Fortunately,two standards were developed and havebeen adopted by the industry.

The two standards are: VESA (Video

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Figure 3. In some newer IBM compatible computers, an additional 124 -pin, 0.05 -inch socket ismounted in I ne with the ISA connectors and provides access to the local bus.

TABLE 2

16 BIT ISA BUS EXTENSION CONNECTIONSPin Number 1/0 SignalCIC2C3C4C5C6C7C8C9CIOCI IC12CI3CI4C15CI6C17CI8

DID2D3D4D5D6D7D8D9DIODI 1DI7DI3D14D15D16DI7DI8

O0I/OI/OI/OI/OI/OI/OI/OI/O

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SBHELA23LA22LA2ILA20LAI9LAIRLAI7MEMRMEMWSDO8SDO9SDIOSDI 1SDI2SDI3SD14SDI5

MEMCS161/OCS 16IRQI0IRQI IIRQI2IRQI5IRQI4DACKODRQODACKSDRQ5DACK6DRQ6DACK7DRQ7+5VMASTERGND

Signal DescriptionSYSTEM BUS HIGH ENABLEUNLATCHED ADDRESS BIT 23UNLATCHED ADDRESS BIT 22UNLATCHED ADDRESS BIT 21UNLATCHED ADDRESS BIT 20UNLATCHED ADDRESS BIT 19UNLATCHED ADDRESS BIT 18UNLATCHED ADDRESS BIT 17MEMORY READMEMORY WRITEDATA BIT 8DATA BIT 9DATA BIT 10DATA BIT IIDATA BIT 12DATA BIT 13DATA BIT 14DATA BIT 15

MEMORY 16 -BIT CHIP SELECTI/O I6 -BIT CHIP SELECTINTERRUPT REQUEST 10INTERRUPT REQUEST 1 I

INTERRUPT REQUEST 12INTERRUPT REQUEST 15INTERRUPT REQUEST 14DMA ACKNOWLEDG 0DMA REQUEST 0DMA ACKNOWLEDGE 5DMA REQUEST 5DMA ACKNOWLEDGE 6DMA REQUEST 6DMA ACKNOWLEDGE 7DMA REQUEST 7+5 VOLTSMASTERGROUND

Table 2. Sixteen -bit ISA bus extension connections.


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VI. LOCAL BUS 32 BIT EX TENSION CONNECTIONSl'in Number I/O Signal Signal DescriptionAI I/O DATO1 DATA BIT IA2 I/O DATO3 DATA BIT 3A3 - GND GROUNDA4 I/O DATO5 DATA BIT 5A5 I/O DATO7 DATA BIT 7A6 I/O DATO9 DATA BIT 9A7 I/O DATI I DATA BIT IIA8 I/O DATI3 DATA BIT 13A9 I/O DATI5 DATA BIT 15A10 - GND GROUNDAll I/O ATI7 DATA BIT 17AI2 I Vcc +5 VOLTSAI3 I/O DATI9 DATA BIT 19Al4 I/O DAT2I DATA BIT 21Al5 I/O DAT23 DATA BIT 23Al6 I/O DAT25 DATA BIT 25A 1 7 - GND GROUNDAl8 I/O DAT27 DATA BIT 27Al9 I/O DAT29 DATA BIT 29A20 I/O AT3I DATA BIT 31A2I I/O ADR30 ADDRESS BIT 30A22 I/O ADR28 ADDRESS BIT 28A23 I/O ADR26 ADDRESS BIT 26A24 - GND GROUNDA25 I/O ADR24 ADDRESS BIT 24A26 I/O ADR22 ADDRESS BIT 22A27 I V + 5 VOLTSA28 1/0 ADR20 ADDRESS BIT 20A29 I/O ADRI8 ADDRESS BIT 18A30 I/O ADRI6 ADDRESS BIT 16A3I I/O ADRI4 ADDRESS BIT 14A32 I/O ADRI2 ADDRESS BIT 12A33 I/O ADRIO ADDRESS BIT 10A34 I/O ADRO8 ADDRESS BIT 8A35 - GND GROUNDA36 I/O ADRO6 ADDRESS BIT 6A37 I/O ADRO4 ADDRESS BIT 4A38 0 WBACK CACHE WRITE BACK. RESERVED USEA39 110 BEO BYTE ENABLE 0A40 I V +5 VOLTSA4I I/O BEI BYTE ENABLE IA42 I/O BE2 BYTE ENABLE 2A43 - GND GROUNDA44 I/O BE3 BYTE ENABLE 3A45 I/O ADS ADDRESS DATA STROBEA46 - KEY KEYA47 - KEY KEYA48 I/O LRDY LOCAL READYA49 I/O LDEV«X» LOCAL DEVICEA50 0 LREQ«X» LOCAL REQUESTA51 - GND GROUNDA52 I/O LGNT LOCAL BUS GRANTA53 I V, + 5 VOLTSA54 0 ID2 CPU IDENTIFIER PIN 2A55 0 ID3 CPU IDENTIFIER PIN 3A56 0 ID4 CPU IDENTIFIER PIN 4A57 0 LKEN LOCAL CACHE ENABLEA58 I/O LEADS LOCAL EXT ADDRESS STROBEA59 - N.C. NO CONNECTIONA60 - N.C. NO CONNECTIONA61 N.C. NO CONNECTION

Table 3. VL local bus 32 -bit extension connections.

Electronics Standards Association) VLbus specification, currently the most pop-ular, and the PCI, Peripheral ComponentInterconnect standard developed by Intel.

The VESA standardThe VL, or VESA Local, standard was

introduced in August of 1992 and caughton very quickly. Designed around the80486 microprocessor's local bus, thestandard was easy and inexpensive to im-plement. This translated into low cost tothe consumer and made it a very attrac-tive upgrade.


Pin Number I/O Signal Signal DescriptionA62 - N.C. NO CONNECTIONBI I/O ATOO DATA BIT 0B2 I/O DATO2 DATA BIT 2B3 I/O DATO4 DATA BIT 4B4 I/0 DATO6 DATA BIT 6B5 I/O DATO8 DATA BIT 8B6 - GND GROUNDB7 I/O DATIO DATA BIT 10B8 /0 DATI2 DATA BIT 12B9 I V + 5 VOLTSB I 0 I/O DAT14 DATA BIT 14BII I/0 DATI6 DATA BIT 16B12 I/0 DATI8 DATA BIT 18BI3 I/O DAT20 DATA BIT 20B14 - GND GROUNDBI5 I/0 DAT22 DATA BIT 22B 16 I/O DAT24 DATA BIT 24BI7 I/O DAT26 DATA BIT 26B 18 I/O DAT28 DATA BIT 28B19 I/O DAT30 DATA BIT 30B20 I V + 5 VOLTSB21 I/O ADR3I ADDRESS BIT 31B22 - GND GROUNDB23 I/O ADR29 ADDRESS BIT 29B24 I/O ADR27 ADDRESS BIT 27B25 I/O ADR25 ADDRSSS BIT 25B26 I/O ADR23 ADDRESS BIT 23B27 I/O ADR2I ADDRESS BIT 21B28 I/O ADRI9 ADDRESS BIT 19B29 - GND GROUNDB30 I/O ADRI7 ADDRESS BIT 17B31 I/O ADR15 ADDRESS BIT 15B32 I V + 5 VOLTSB33 I/O ADR13 ADDRESS BIT 13B34 I/O ADRII ADDRESS BIT 11B35 I/O ADRO9 ADDRESS BIT 9B36 I/O ADRO7 ADDRESS BIT 7B37 I/O ADRO5 ADDRESS BIT 5B38 - GND GROUNDB39 I/O DRO3 ADDRESS BIT 3B40 I/O ADRO2 ADDRESS BIT 2B41 - N.C. NO CONNECTIONB42 0 RESET SYSTEM RESET FOR VL DEVICESB43 I/O D/C DATA/CODE STATUS (IDENTIFY)B44 I/O M/I0 MEM OR I/O STATUS (IDENTIFY)B45 I/O W/R READ/WRITE STATUS (IDENTIFY)B46 - KEY KEYB47 - KEY KEYB48 0 RDYRTN READY RETURNB49 - GND GROUNDB50 I IRQ9 INTERRUPT REQUEST 9B51 I/O BRDY BURST READYB52 I/O BLAST BURST LASTB53 0 1DO CPU IDENTIFIER PIN 0B54 0 IDI CPU IDENTIFIER PIN IB55 - GND GROUND1356 0 LCLK LOCAL CPU CLOCKB57 I V + 5 VOLTSB58 I/O LBSI6 LOCAL BUS SIZE=I 6 BITSB59 - N.C. NO CONNECTIONB60 - C. NO CONNECTIONB61 - N.C. NO CONNECTIONB62 N.C. NO CONNECTION

The VL bus connects the peripheralsdirectly to the microprocessor's bus via a124 -pin, 0.05 -inch connector (Table 3).This places quite a load on the micropro-cessor's address and data lines and limitsthe number of expansion connectors totwo. Some motherboards add buffering to

the bus, which increases the connectorcount to three. Electrical characteristicsof the connectors determine the maxi-mum bus speed.

If a device is integrated into the moth-erboard, speeds as high as 66MHz can beobtained. If one device is inserted into a

local bus connector the maximum speedis reduced to 40MHz. The speed is thenfurther reduced to 33MHz when a seconddevice is added. Capacitance loading ofthe connector limits the expansion slotsto three. For most consumers this is not aproblem, since video and hard drive con-trollers are currently the only productsavailable to access the local bus.

The PCI standardThe PCI standard was designed to work

with high -end chips beyond the 80486,such as Intel's Pentium processor and oth-er, non -Intel, chips. As in the case of theVL standard it uses the 124 -pin 0.05 -inchconnector. However, it multiplexes theaddress and data lines, which limits thesystem speed to 33MHz (Table 4). Unlikethe VL bus standard, PCI does not con-nect the peripheral directly to the micro-processor's bus. It creates a separate bususing a controller and accelerator chip set.This technique allows the PCI standard tobe microprocessor independent.

Another attractive feature of PCI isautomatic peripheral configuration. Thisallows the end user to install expansioncards without worrying about such thingsas memory addresses, DMA channels andIRQ settings. In addition, the PCI stan-dard can support up to six peripherals.The main disadvantage to PCI over VL ishigh cost. This could change as the PCIstandard becomes more popular.

Although the two standards are techni-cally not compatible they have some sim-ilarities. Both designs use the additional0.05 -inch pin spacing socket made popu-lar by IBM in its Micro Channel Archi-tecture. The MCA style connector ismounted in -line with the existing ISAconnectors. Both designs are also up-gradeable from 32 bits to 64 bits to workwith Intel's new Pentium processor.

Achieving high-speed data transferBoth VL and PCI local bus technology

use a process called burst transfers totransfer data at high speed. In a normalexchange of data between devices, thetransmitting device first sends an addressto the receiving device and then followswith data. The process is simply repeat-ed over and over until all the data is sent.Burst transfers eliminate the repetitiveaddress step by assuming all addresses are


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Soldering iron/torch kitPhilips ECG has announced that its

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The product is a compact, light-weight, hand-held tool that features asee-through refillable butane tank, atemperature control for accurate adjust-ment of tip temperature, and a built-inigniter. Applications for this tool includeelectrical/electronic circuit repair, form-ing heat -shrink tubing, light gaugewelding, brazing, light plumbing, jew-elry and eyeglass frame repair, modelbuilding, arts and crafts, and thawingfrozen locks.

The kit includes the soldering iron/torch, a solder tip, blow torch tip, hotknife tip, heat blower tip, metal safetystand, a cleaning pad, spare flints and ahalf -ounce of 60/40 rosin core solderall encased in a heavy-duty, fitted car-rying case. Additional tips are optional-ly available.


TABLE 4PCI LOCAL BUS 32 BIT EXTENSION CONNECTIONSPIN 110 SIGNAL SIGNAL DESCRIPTIONAl TRST TEST RESETA2 +I 2V + 12 VOLTSA3 TMS TEST MODE SELECTA4 TDI TEST DATA INPUTA5 +5V +5 VOLTSA6 0 INTA NTERRUPT AA7 0 INTC INTERRUPT CA8 +5V + 5 VOLTSA9 NA NA RESERVEDA10 I/O +5V + 5 VOLTSAll NA NA RESERVEDAI2- GND GROUNDA13 GND GROUNDA14 NA NA RESERVEDA I 5 I RST RESETAl6 I/O +5V + 5 VOLTSA17 I GNT GRANT (BUS MASTER ONLY)A18 GND GROUNDAl9 A NA RESERVEDA20 I/O AD30 ADDRESS/DATA BIT 30A21 I +3.3V + 3.3 VOLTSA22 I/O AD28 ADDRESS/DATA BIT 28A23 I/O AD26 ADDRESS/DATA BIT 26A24 GND GROUNDA25 I/O AD24 ADDRESS/DATA BIT 24A26 I IDSEL INITIALIZATION DEVICE SELECTA27 I 3.3V +3.3 VOLTSA28 I/O AD22 ADDRESS/DATA BIT 22A29 I/O AD20 ADDRESS/DATA BIT 20A30 GND GROUNDA31 I/O ADI8 ADDRESS/DATA BIT 18A32 I/O ADI6 ADDRESS/DATA BIT 16A33 1 +3.3V +3.3 VOLTSA34 I/O FRAME CYCLE FRAMEA35 GND GROUNDA36 I/O TRDY TARGET READYA37 GND GROUNDA38 I/O STOP STOPA39 I +3.3V +3.3 VOLTSA40 I/O SDONE SNOOP DONEA41 I/O SBO SNOOP BACKOFFA42 GND GROUNDA43 I/O PAR PARITYA44 I/O ADI5 ADDRESS/DATA BIT 15A45 I +3.3V +3.3 VOLTSA46 I/O ADI3 ADDRESS/DATA BIT 13A47 I/O ADI I ADDRESS/DATA BIT I I

A48 GND GROUNDA49 1/0 ADO9 ADDRESS/DATA BIT 9A50 KEY KEYA5I KEY KEYA52 I/O C/BEO BUS COMMAND/BYTE ENABLE 0A53 I +3.3V +3.3 VOLTSA54 I/O ADO6 ADDRESS/DATA BIT 6A55 I/O ADO4 ADDRESS/DATA BIT 4A56 GND GROUNDA57 I/O ADO2 ADDRESS/DATA BIT 2A58 I/O ADO() ADDRESS/DATA BIT 0A59 I/O +5V 5 VOLTSMO I/O REQ64 REQUEST 64 -BIT TRANSFERMl +5V +5 VOLTSA62 +5V +5 VOLTS

Table 4. PCI local bus 32 -bit extension connections.

consecutive. The initial address is sent tothe receiving device followed by a "burst"of data. The receiving device incrementsthe addresses as it receives the data. Thelength of a data burst is unlimited, how-

ever, each new "burst" of data requires anew address.

Another technique called "bus master-ing" allows data to be exchanged betweenbus devices without using the micro -


PIN I/O SIGNAL SIGNAL DESCRIPTIONB1 I - I 2V -12 VOLTSB2 I TCK TEST CLOCKB3 GND GROUNDB4 0 TDO TEST DATA OUTPUTB5 I +5V +5 VOLTSB6 I +5V +5 VOLTSB7 NIB INTERRUPT BB8 0 INTD INTERRUPT DB9 0 PRSNTI EXPANSION CARD PRESENT IB I 0 NA NA RESERVEDB I I PRSNT2 EXPANSION CARD PRESENT 2B12 - GND GROUNDBI3 - GND GROUNDB14 NA NA RESERVEDB15 - GND GROUNDB16 I CLK CLOCKB17 - GND GROUNDB18 0 REQ REQUEST (BUS MASTER ONLY)B19 I/O +5V +5 VOLTSB20 I/O AD3I ADDRESS/DATA BIT 31B21 I/O AD29 ADDRESS/DATA BIT 29B22 - GND GROUNDB23 I/O AD27 ADDRESS/DATA BIT 27B24 I/O AD25 ADDRESS/DATA BIT 25B25 I +3.3V 3.3 VOLTSB26 I/O C/BE3 BUS COMMAND/BYTE ENABLEB27 I/O AD23 ADDRESS/DATA BIT 23B28 - GND GROUNDB29 I/O AD2I ADDRESS/DATA BIT 21B30 I/O AD19 ADDRESS/DATA BIT 19B31 I +3.3V +3.3 VOLTSB32 I/O ADI7 ADDRESS/DATA BIT 17B33 I/O C/BE2 BUS COMMAND/BYTE ENABLEB34 - GND GROUNDB35 I/O IRDY INITIATOR READYB36 I +3.3V 3.3 VOLTSB37 I/O DEVSEL DEVICE SELECTB38 - GND GROUNDB39 I/O CLOCK CLOCKB40 I/O PERR PARITY ERRORB41 I +3.3V +3.3 VOLTSB42 I/O SERR SYSTEM ERRORB43 I +3.3V +3.3 VOLTSB44 I/O C/BEI BUS COMMAND/BYTE ENABLE 1B45 I/O ADI4 ADDRESS/DATA BIT 14B46 - GND GROUNDB47 I/O ADI2 ADDRESS/DATA BIT 12B48 I/O ADIO ADDRESS/DATA BIT 10B49 - GND GROUNDB50 - KEY KEYB51 - KEY KEYB52 /0 ADO8 ADDRESS/DATA BIT 8B53 I/O ADO7 ADDRESS/DATA BIT 7B54 I +3.3V +3.3 VOLTSB55 I/O ADO5 ADDRESS/DATA BIT 5B56 I/O ADO3 ADDRESS/DATA BIT 3B57 - GND GROUNDB58 I/O ADOI ADDRESS/DATA BIT 1B59 I/O +5V + 5 VOLTSB60 I/O ACK64 ACKNOWLEDGE 64 -BIT TRANSFERB61 I +5V + 5 VOLTSB62 I +5V + 5 VOLTS

processor or system memory. A bus"master" controls which devices haveaccess to the bus and prevents interfer-ence between devices. Both VL and PCIcan support up to three bus masters.

Computers that can be upgradedto local bus

Any 80286, 80386, or 80486 systemwith a desktop or tower case can be up-graded with a local bus motherboard.

FREE

Parts Express is afull -line distributor ofelectronic parts andaccessories, gearedtoward the consumerelectronics industryand the technicalhobbyist. We stock anextensive line ofreplacement parts forTV and VCR repair.Call for your FREE 188page catalog today.

PartsEasas

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1-800-338-0531The free catalog is sent via bulkmail to U.S. addresses. Forexpress delivery, please send$2.50 to cover 1st classpostage. Foreign destinationcustomers, please send $5.00to cover postage.

340 E. First St.,Dayton, Ohio 45402-1257



Figure 4. A local bus expansion card connects to the ISA and local bus connectors.

Test Your ElectronicsKnowledgeAnswers to the quiz

(from page 27)

1. C. Power is the time RATE of metic Logic Unit (ALU) in a micro -doing work or using energy. processor.

2. No. A pure sine wave has no har-monic frequencies.

3. C. The neon lamp cannot glowbecause the applied voltage is toolow. It is necessary to have at least60V to start neon lamps.

4. A. By definition.

5. B. The voltage gain is less thanone. There is current gain.

6. It is the symbol for the Arith-

7. In a series -wound motor, thearmature and field windings are con-nected in series. If this type of motoris operated without a mechanicalload, its speed will increase until it isdestroyed.

8. D. The product of the gain andbandwidth is a constant.

9. D. By definition.

10. D. The full-scale deflectioncurrent is equal to the reciprocal ofthe ohms -per -volt rating.

(Slim line cases are usually proprietarysystems and require the original vendor'shardware to fit properly). In addition, itmay be necessary to upgrade the powersupply to a 200W or 250W unit if a small-er power supply is present in the system.

The old or defective motherboard is re-moved and the local bus board is installedin its place. The local bus expansion cardsare then inserted into their special slots.A local bus expansion card connects to theISA and local bus connectors (Figure 4).

Software drivers are usually includedwith the expansion cards or may be incor-porated with a particular program's soft-ware. Check the expansion cards docu-mentation for details.

Choosing a local bus systemUpgrading to local bus can provide sig-

nificant system performance increases.Two questions remain: Who can benefitfrom local bus? Which system should youchoose or recommend to your customer?

The biggest benefit will come to thegraphics -based program user. However, aDOS -based program user will see someimprovement as well. The price of a VLmotherboard makes it impossible to ig-nore when upgrading or repairing an80286 or 80386 PC. The difference inprice of an 80486 ISA motherboard andan 80486 VL motherboard is insignifi-cant. (Many vendors don't even list 80486ISA motherboards on their price sheets.)In addition, VL peripheral expansioncards are competitive in price with theirISA counterparts.

Either VL or PCI can increase the per-formance of a PC. Which should youchoose or recommend to your customer?VL is dominating the market right now,because support is good and it is inex-pensive. A number of major manufactur-ers support PCI. This seems to indicatefuture support for this standard. PCI ismore expensive to implement which in-creases the price of the PC, but may offeradvantages in the future. As with any con-sumer product, as popularity increasesthe prices should drop.

VL seems the choice for now. As withany new consumer product we will haveto watch the industry and make our deci-sion based on current conditions and fu-ture projections.

If a customer comes to you complain-ing of slow screen drawing or data trans-fer, tell them that they need to get on thebus-the local bus.


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Catalog of electronic partsand components

The MCM Catalog contains over20,000 high -demand parts and compo-nents-more than 1,000 of them intro-duced for the first time in this latest edi-tion. Among the categories of productsoffered are: semiconductors, televisionparts, power supplies, home securityalarms, telephone parts and accessories,connectors, tools, batteries, speakers,VCR parts and more; including the com-pany's own line of value -priced TENMAtest equipment. The company has ex-panded its lines of computer and cellularproducts and has introduced a selectionof appliance repair parts.


Catalog of test equipment,tools and supplies

This 244 -page catalog from ContactEast lists test instruments and tools forengineers, managers, technicians, andhobbyists. Featured are quality productsfrom brand -name manufacturers for test-ing, repairing, and assembling electronicequipment. Product highlights includenew DMMs and accessories, solderingtools, custom tool kits, EPROM program-mers, power supplies, ELF meters, help-ful reference books, breadboards, scopemeters, datacom tools and testers, adhe-sives, measuring tools, precision handtools, portable and bench top digital stor-age scopes. Also included are the compa-ny's lines of communication test equip-ment, soldering/desoldering systems,

static protection products, ozone safecleaners, magnifiers, inspection equip-ment, workbenches, cases and more.


PC replacement parts catalogon floppy disk

PC Parts Express announces the avail-ability of their catalog of replacementparts for personal computers and periph-erals on floppy disk. The program con-sists of three basic modules that allow theuser to perform three separate but relatedoperations. The "Spare parts catalog itemsearch" segment allows the user to searchthe data base to determine if a needed partis available from this supplier. The "Orderprocessing" segment allows the user toautomatically generate an order as hesearches through the parts listed andselects those he wants to order. The"Utilities" program segment containsmodules that allow the customer to set upand/or change his ordering information,make changes to the printer setup, a noteon using the catalog, and a complete tuto-rial on searching for parts and orderingusing the catalog. The catalog containsreplacement parts for products by thesemanufacturers: AST, Canon, Compaq,Epson, Fujitsu, HP, IBM, Kingston,Micro House, NEC, Okidata and Toshiba.The program allows the user to look upthe parts needed, and as he does so, auto-matically enter them into an order formwhich can then be printed out and mailedto the company, or faxed directly usingthe computer's fax/modem, if it has one.The catalog comes on one compressedfloppy disk. When expanded it requiresnearly 8 Mbytes of hard disk space.


Production equipment catalogNow available is the Eraser Company's

new 144 -page, full -color, 1994 catalog,which includes new products used forwire stripping, cutting, dereeling, twist-ing, soldering, etc.

The catalog is divided into ten sections,covering all aspects of wire processingand component lead preparation. Severaltechnical guides present information onchoosing the proper equipment for anindividual application.


irnth ,,,, Pcnw,

t /1,N,folfl.

.40I, Pik ..rot yr, Guicit

Catalog describespower protection products

A new, full -line "Power Protection"catalog is now available from EFI.

This 24 -page, full -color, long -formproduct catalog describes a facility -widesolution to power and data line protectionfrom transient voltages and other powerproblems typically found in commercial,industrial and medical facilities. In addi-tion to in-depth product descriptions, thecompany's patented product technolo-gies and value-added warranty programsare fully described.

The catalog also includes all availablemodel numbers for over 50 categories ofpower protection products and services.Complete technical specifications are in-cluded, as are typical applications, impor-tant features, advantages and benefits,and full ordering guides for all products.


Application note explains harmonicsBMI's new application note #230,

"Harmonics: Sources, Symptoms, andSolutions," explains the causes and ef-fects of harmonics, how to detect andmeasure harmonics, as well as how toavoid and solve the resulting problems.

The five -page application note in-cludes two case studies on the hazardouseffects of harmonics, one featuring atransformer explosion, the other, CRTflicker. The application note also presentsinstruments for use in harmonics detec-tion and measurement.



Correction to the article

"Simple power supply and probe adapteraid testing"By Roger D. Redden

In the February 1994 issue of Elec-tronic Servicing & Technology we pub-lished an article entitled "Simple powersupply and probe adapter aid testing."There was an omission in one of thegraphics that accompanied that article.

The power supply was described thisway: "The power supply becomes use-ful when plugged into an isolated, vari-able ac source, such as an isolationtransformer followed by a variable trans-former. When plugged into such asource, this power supply can providefrom OVdc to more than 150Vdc,

depending on the amount of currentdrawn and the top voltage of the variabletransformer used. This makes it useful totest a suspected IHVT at its operatingvoltage level, or to check a zener diodewith a voltage rating up to about 150Vdc.

Caution! This power supply is capa-ble of supplying an output that could belethal! Do not plug it directly into an acoutlet. You must use it with an isolationtransformer. To remind myself, I at-tached a label near the plug with theprinted warning, 'Isolated Only.'"

Figure 1 shows the circuit that accom-

panied that article. The power supplywill work fine with the circuit as shown.Unfortunately, the capacitor will hold acharge fora long time so that if you touchthe outputs even with the unit unplugged,you could receive an uncomfortableshock.

If you build this power supply, be sureto add the bleeder resistor as shown inFigure 2. With this resistor in the circuit.the capacitor voltage will bleed awaythrough the resistor in a relatively shortperiod of time.

F1

2A

D1

2.5A1000V

C1

100uF250V

1511

low

C2100uF250V

F21.25A

Our GND

Figure 1.

Figure 2.


ClassifiedClassified advertising is available by the word or per column inch.By -the word. $1.65 per word, per insertion, pre -paid Minimum charge is $35 per insertion. Initials and abbreviations count as full words. Indicate free category head-ing (For Sale, Business Opportunities, Miscellaneous, Wanted). Blind ads (replies sent to ES&T for forwarding) are $40 additional. No agency discounts are allowedfor classified advertising by the word. Contact Linda Romanello at 516-681-2922 to place your classified ad (by-the-worch. Mastercard, VISA, American Express andDiscover are accepted for FAX or mail orders.Per column Inch (classified Display): $235 per column inch, per insertion, with frequency discounts available, 1" minimum, billed at 1/4" increments after that 10"maximum per ad. Blind ads are $40 addition. Reader Service Number $25 additional to cover processing and handling costs. (Free to 4 -inch or larger ads.) For moreinformation regarding classified display advertising please call 516-681-2922. Optional color (determined by magazine) $150 additional per insertion.

Send your order, materials and payments to:Electronic Servicing & Technology, 76 North Broadway, Hicksville, New York 11801

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Tek 442 35MHz scope w/TV Trigger $269, Tek2215 60MHz scope w/TV Trigger $489. Call for list-ing of our used equipment. We buy surplus equip-ment. Test Equipment Sales (603) 434-2544.

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TV CASE HISTORIES: Booklet with 2,150+histories. Satisfaction assured. Only $45 (plus$2.90 for 2 -day priority). Mike's Repair Service,P.O. Box 217. Aberdeen Proving Ground, MD21005. Same mailing address 30 years. SendSASE for samples. 410-272-4984, 11am-9pm.

Sencore SC61 Waveform Analyzer. Looks &works like new. Phone 913-738-3332.

Sencore VC93 all format VCR Analyzer. Usedslightly. Complete with manuals, probes, and ship-ping carton. 518-398-5684.

FOR SALE

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TEST EQUIPMENT BOUGHT & SOLD: OSCIL-LOSCOPES, ETC. 1-408-738-4206. FAX 1-408-736-6946.

VHS -VCR Repair Solution Sets I - IX. Each con-tains 150 symptoms and cures, cross referencechart, free assistance, $19.95 each, all nine$49.95. Visa/MC. Eagle Electronics, 52053Locks Lane, Granger, IN 46530.

Earn $$$ Repairing Zenith TV's to componentlevel -now over 1000 models 1983-1993.Guaranteed effective and reliable cost cuttingsymptom/cure format. Buy manual and receiveFREE report, "Repair Shorted CRT's Fast" (rasterone co.or) $89.95. Demo Sampler $19.95. ZMEX,807 Queen Palm Lane, Sarasota, FL 34243.

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REDUCED 85%. Diehl Mark III $69, Diehl Mark VHorizontal circuit tester $179. New. Conductivecoating for remote control keypads $9.99 ppd.WEEC, 2411 Nob Hill Road, Madison, WI 53713.608-238-4629, 608-233-9741.

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Sencore Video Analyzer system-VA62A-ST65-RG67-VC63-NT64. Just Factory calibrated-New$7000, sell $2600. 415-363-8691. Chris.

*SERVICE MANAGERS & TECHNICIANS' National company with regional service centers inNorth Carolina and Missouri will be opening a newoperation in Fontana, CA. Positions available inTV, VCR, AUDIO, and SMALL APPL. Sendresume with salary history to H.M. ServiceCenter, P.O. Box 64189, Fayetteville, NC 28306.Attn: Service Supervisor.

Sencore VR62A Universal Video Analyzer,Sencore CR70 CRT Analyzer. Best offer! 1-800-229-9826.

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Readers' ExchangeReaders' Exchange has been reinstated as a free

service.The following restrictions apply to Readers'

Exchange: Only individual readers may use Readers'

Exchange, and items must be restricted to thosethat are ordinarily associated with consumer elec-tronics as a business or hobby. If you're in busi-ness to sell the item(s) you want to offer for sale,the appropriate place for your message is in a paidadvertisement, not Readers' Exchange.

Readers' Exchange items must be restrictedto no more than three items each for wanted andfor sale, and may be no more than approximatelyfour magazine column lines in length (about 20words).

All submissions must be typed or printedclearly!

Send your Readers' Exchange submissions to:

Readers' ExchangeElectronic Servicing &

Technology76 N. Broadway

Hicksville, NY 11801

WANTED

Service manual/schematic for Microtechmodel 555L reel-to-reel tape deck. Will buyor copy & return. Contact William W. Teasley,15213 NE 27th Ave., Vancouver, WA 98686,(206) 574-0534.

Information on legitimate companies that payto assemble electronic boards in the home.Contact Glenna G. Marsh, Rt. I , Box 239, NewMilton WV 26411.

Operating and service literaure (schematic)for Amphenol Color Commander, model 860.Also source for 2N1180 transisitors. ContactT. Mueller, 345 Cherokee, Ridge, Athens, GA30606, (707) 546-5533.

Sencore VA62A with VC63 VCR Tester andNT64 NTSC Pattern Generator. All cables andmanuals, used very little. $2500.00. Call 509-483-9440, 9:00 a.m. to 5:00 p.m. WST.

Picture tube for Broksonic 5 inch color TV,model cert. 2610 UL. 150AYB22. Contact M.Mitchell, 1665 Brownstone #3, Toledo, OH43614.

Chrysler car radio schematics for past 10years, fiche, paper, or copies OK; also needSams 2313-2334, 2338, 2369-2389, 2460-2557, and JVC HR -7300U or Tatung VRH-8200U VHS service manual. Contact RandyBaeseman, 8301 S. Mountain Rd., Wausau,WI 54401, (715) 359-6604 (6 p.m. to mid-night).

Flyback 334P09403 for Mitsubishi, modelCK2582. Contact Dales TV, Rt. 1, Box 236,Mountainview, MO 65548, (417) 934-6655.

JVC VCR service manuals. Contact TrumanMcGregor, 3601 Jefferson Ave., Texarkana,AR 75502, (501) 773-6488.

Schematic for (or ability to borrow) MobileAuthority Power Supply, model 810ZX. Alsofront panel glass for Frigidaire Flair range,mode148C27912. Contact Warren Shukis,1479 Prince Edward Way, Sunnyvale, CA94087, (510) 651-5112.

Sams Photofacts, 2400 to present, any quali-ty, will pay C.O.D. Contact Reynolds TV &Video Service, 3510 Adams Ave., San Diego,CA 92116, (619) 284-9239.

Microfiche reader, Variac, VCR service man-uals. Contact Nick, (717) 383-3975.

Owner's manual or copy for Toshiba VCRmodel M-6000. Contact Ron Purkhiser, 56Oakhurst Dr., Munroe Falls, OH 44262, (216)688-6624.

Schematic for Apple monitor ModelA2M2056 and same for other Apple monitors;meter for Sencore CR168 CRT tester. ContactSteve Baker, 164 River Road, Hackettstown,NJ, (201) 927-0949.

Schematic for color TV Contec Model MN -1347, chassis N13-0,8. Contact DonaldStevens, 1005 N. Brookfield. South Bend, IN46628, (219) 233-3746.

Will pay for flyback transformer for MitsubishiTV, model CK2582, p/n 334P09403, no longeravailable from Mitsubishi. Contact Dales TV,Rt. 1 Box 236, Mountainview, MO 65548, (417)934-6655.

RCA yoke 150468, Magnavox cartridge560355. Contact Frank Szwanek TV, 303Nothe Blaine, Box 237, Mullen, NE 69152.

Will pay for schematic, copy, or micorfiche,plus shipping for Fisher stereo model MC708.Contact Augustine's TV & Radio Service,3129 Earl St., Laureldale, PA 19605, (610)929-8850.


Will pay top dollar for a lA (slow blow) fusefor a Dumont 2100G oscilloscope. ContactMerrill Lannen, 6206 Thonotosassa Rd.,Plant City, FL 33565, (813) 986-6383.

FOR SALE

Leader dual trace 10 MHz oscilloscope,$200.00; B&K 1077 television analyst,$350.00; B&K 415 sweep/marker generator$300.00. Original box, all excellent condition.Contact John, (201) 432-7635.

DMM reads current to 10A, resistance to20Mi2 acV & dcV new, $49.00; capacitancedigital tester, tests to 2200 Mfd, hardly used,$45.00; VCR head for Magnavox (used onmost Magnavox VCRs), new, $19.00.Contact Joe Oracki, 3502 E. Northern Pkwy.,Baltimore, MD 21206, 1-(410) 254-0284.

Sencore PS29 scope, RF demodulator probe,RCA WM54 1 A dual tracer, Sencore NP229needlepoint. All for $500.00 or best offer.Much more tip top shape for list. Contact FredIngersoll, 6845 Lathers, Garden City, MI48135. Send legal size S.A.S.E.

RCA service manuals (1955-1970), $6.00each or all 3 for $15.00 plus shipping; RCApict-o-guide manuals, vol. 1 & 2 (1949), $5.00for both plus shipping; Electronic Technicianmagazines (1965 to 1976), $.50 each or all 41for $18.00 plus shipping; Tab Books TV ser-vice manuals (different makes, 1970-1972),$3.00 each or all 13 for $30.00 plus shipping;TV & radio tube test sockets, $1.50 each plusshipping; Radio Amateur's Handbook (1959),$5.00 plus shipping. Contact (412) 483-3072.

Sams Photofacts; RCA Service DataConsumer Electronic Products books(1967-1978). Contact Ann Bichanich (Jays),15 1/2 W Lake St., Chisholm, MN 55719, 1-(218) 254-4421.

Sencore VA48 analyzer, $395.00; SencorePS163 scope, $99.00; B&K 415 sweep -mark-er gen., $95.00. Complete manuals and cables.Shipping extra. Contact Val Obal, 3201 So.73rd St., Omaha, NE 68124, (402) 393-0459.

Photofacts 188-222 & 2562033; auto radiomanuals AR19-300, $1.00 each if you take all;Zenith test rig, 800-880, $50. Contact KeithsRadio, Box 95, Belleville, NY 13611, (315)846-5123.

Zenith service literature 1976 to 1993,$1000.00 plus shipping; five thousand radioand TV tubes new in boxes, $1500.00 plusshipping. Contact Dales TV, Rt. 1, Box 236,Mountainview, MO 65548, (417) 934-6655.

Over 300 new tubes in boxes, old Sams TVmanuals (approx. 100), make offer. ContactNick, (717) 383-3975.

Sencore DVM37 digital voltmeter, $75.00;VIZ (RCA) WWV-703B 220-240 V line mon-itor, $45.00; ESR meter, $95.00. Contact(703) 525-2382.

TA3000 and 30 adapters, $20.00 plus ship-ping. Contact M.E. Andrews Jr., P.O. Box 91,Exeter, RI 02822.

Good CTC 130 chassis complete with tuner -yoke for RCA X25621EB 25.8 kV, $90.00post paid. Contact W.F. Smith, 1054 S.Elizabeth, Kokomo, IN 46902.

Pix tube push -on curcuit board, Philips p/n483526597092, for Magnavox, Philco,Sylvania, Philips TVs. New, in sealed enve-lope, no longer need, $8.00. Contact W.Krebs, P.O. Box 3765, Silverdale, WA 98383-3765.

Tektronix 2245A 4-ch., 100 -MHz digitalreadout scope w/ pouch & cover, tilt swivelbase, 4 probes including high voltage & ser-vice manual, like new, recent factory calibra-tion, $2000.00 or best offer. Also TektronixCMC250 2-ch., 8 -digit 1.3 GHz multifunctionfrequency counter, new condition, in originalbox w/manual. $400.00 or best offer. ContactBruce, ( 516) 437-2277.

B&K TV equipment 1077B TV analyst, 415sweep marker generator, 1477 dual traceoscilloscope, 465 CRT tester, 520 transistortester, 283 digital multimeter, 1245 color gen-erator, $1200.00 plus shipping. Contact DalesTV, Rt. I , Box 236, Mountainview, MO 65548,(417) 934-6655.

Set of ES&T magazines from Nov. 74 to Jan.91 (except Jul. 89), make offer. Contact MikeKrajewski, 20 Criscoe St., Toronto, Ont.,(416) 767-9014 (after 7 p.m.).

Sencore SC61 waveform analyzer, $1200.00,or trade for VA62 video analyzer. Contact 1-(515) 295-9344.

Sams Manuals; modular hi-fi tape recorder,transistor radio, autoradio, CB radio andassorted other books. Contact A. D. Bruck, Rt.#1, Box 3 56, Cleveland, VA 24225, (703) 889-5591. Send S.A.S.E. for complete list.

Sencore/IBM electronic management soft-ware complete with all revisions and latestupgrade multi-user version. Originally$3500.00, will sell for $1500.00 or best offer.Contact Marge (409) 935-3321.

Sencore instruments: SC3100, VC93, LC102,PR57, hardly used, going out of business dueto bad health, must sell, all four instruments,$7200.00, individually best offer. ContactTony Talarczyk, R 1 , Box 21, Montgomery,MN 56069.

VCR, camcorder, camera, combo, manufac-turers service manuals, all new. Contact VTS,Inc., 3333 S. Maryland Pkwy., Ste. 8, LasVegas, NV 89109. Send business -sizeS.A.S.E. for complete list.

Motorola car radio service manuals, 1952 &1954; Riders manuals, Vol. 1-XVII; PFReporter magazines, 1963-1973. ContactDean Daleske, 602 11 Ave., Eldora, IA 50627.

Approximately 30 Magnavox (not N.A.P.)TV modules for older color TVs, new, inboxes, $45.00 plus $10.00 shipping. ContactMaurer Radio -TV Service, 29 South 4th St.,Lebanon, PA 17042.

Sencore scope, SC61A (like new) with man-ual, probes, cables, $1495.00 plus UPS.Contact Major, (913) 467-8431/3921.

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Each binder is $9.95 plus $1 S & H ($2.50 outside the US).

Mail all correspondence to:

Electronic Servicing & TechnologyJesse Jones Industries, Dept. EST

499 East Erie Avenue, Philadelphia, PA 19134CHARGE ORDERS: (Minimum $15): AMEX, VISA, MC, DC accepted. Send card name, a. Exp. date.

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Send All Correspondence To:

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FAX 516-681-2926

Advertiser's IndexReader

Page Service AdvertiserCompany Number Number Hotline

Antique Automobile Radio 68 70 800/WE FIX AM

B & K Precision 6 71,72 ....312/889-1448

Den -On Instruments 47 73 800/397-5960

Fluke Corporation BC 19 800/87FLUKE

Howard Electronics 68 74 800/394-1984

International Components Corp..68 75 800/645-9154

lscet 58 817/921-9101

Jensen Tools 45 76 800/426-1194

MICROCARE 53 77 203/585-7912

NESDA 12,41 817/921-9061

PTS Electronics 11 79 800/844-7871

Parts Express 61 78 800/338-0531

Philips ECG 3 81,82 ....800/526-935483,84

Platt Luggage 46 85 800/222-1555

Premium Parts + 12 800/558-9572

RS Electronics IBC 86 800/366-7750

Sams, Howard & Company 49 87 800/428-7267

Sencore IFC 1 800/SENCORE

Sony Service Company 15 88

Sperry Tech 68 89 800/228-4338

Tentel 44 90 800/538-6894

Time Motion Tools 41 91 800/779-8170

Wavetek 5 93 800/854-2708

Wholesale Electronics 68 94 800/351-2233

We'd like to see your company listed here too. Call DianeKlusner at 516/681-2922 to work out an advertisingprogram tailored to suit your needs.

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DuracellJohnson ControlsEvereadyPhilips ECGPowersonicRayovac

Cabinets/Racks/Enclosures

BudPac-Tec

Capacitors/Filters

Cornell DubilierDaleMalloryNIC ComponentsNichiconSchurterTusonix

Chemicals

GC ThorsenMulticoreTech Spray

Connectors/Sockets

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Crystals/OscillatorsDaleStatek

Displays/Optoelectronics

Chicago MiniatureDaktronicsDaleDialightIndustrial DevicesOptrex

Fans/Blowers/Motors

Comair RotronEBMPapst

Superior Electric

Fuses/Circuit Breakers

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Inductors

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Power Supplies

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AgastatAlcoswitchAromatCrydomGuardian ElectricHamlinMagnecraft/MSDPhilips ECGPotter & BrumfieldStruthers-Dunn/MSD

Resistive ProductsAllen BradleyBournsCKEClarostatDaleNIC ComponentsNytronics

OhmiteSpectrolVamistoVRN

Security Equipment

Burle

Semiconductors

Diodes, nc,International RectifierPhilips ECG

Sensors

Micro Switch

Solder & Equipment

American BeautyCooperTools:

tinge'Weller

Denon InstrumentsMulticoreOK Industries

Static Control

Charleswater3M

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AlcoswilchAMPAromatC & KCarlingswitchCherryDialightEECOGrayhillHamlinITWMcGillMicro SwitchSchurterSwitchcraft

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PRO -LINESimpsonTektronixTriplett

Thermisters

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CooperTools:BonneyDiamondEremUngarUticaXcelite

GC ThorsenGreenlee ToolsIdealLeviton3MPaladinPlatt

Transformers

DaleStacoStancorSuperior Electric

Tubes

Richardson (National)Video Display Corp.

UPS & Voltage Control

DeltecSole ElectricSuperior ElectricTripp LiteWaber

Video/Audio

Atlas SoundBogenElectro-VoicePhilips ECGReimOuamShureUniversity Sound

Wire/CableiTubing

AlphaAmphenol Spectra -StripBeldenCarolDearbornWatlow Gordon

Wiring Accessories

BradyDennisonLeviton3MPanduitThomas & Betts


EXECUTIVE OFFICES34443 SchoolcraftLivonia, MI 48153(313) 525-1155 FAX (313) 525-11841-800-366-7750

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NEV YORK OFFICE295 Oser Ave.Hauppauge, NY 11788(516; 231-33131-300-433-8952FAX (516) 231-6372

DISTRIBUTING OVER 200 LINES SINCE 1929

There are copies and then there are

originals. Only Fluke meters - the original

and most copied DMMs in the world - deliver

the safety, quality and value they promise.

They're built tough enough to achieve

C.S.A. and U.L. listings, not to mention the

considerable on-the-job punishment they

endure. Each meter is loaded with features, of

course. But those features are also designed

to work together intelligently, so your job is

easier. Faster. And safer.

If you're going to spend your hard-earned

money on a multimeter, why buy an inferior

copy when you can own an original? See

Fluke's full line of handneld meters and

accessories at your local distributor; or call

1-800-87 FLUKE for the name and number.ORIGINALSFLUKE 87 TRUE Mt' MILT:METER

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Fla.

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FLUKE®© Copyright 1993 John Fluke Mfg Co., inc. P.O. Boo 9090 M/S 250E Everett. WA 98206 U.S.: 206-356-5400

Canada: 416-890-7600 Other Countries: 206-356-5500 AU rights reserved. Ac no. 00381


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