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How

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harp's sweep

circuits

Understanding

decibels andtim

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Learningbout electronics

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November 1983 Electronic Servicing & Technology 1

The how-to magazine of electronics...ieiEtoiiio8

November 1983Volume 3, No. 11

OiOCTitOBiCe .o,...,,.,em

Electronics manuals, specsheets and specificinstruction handbooks areideal sources for updatingyour electronics knowledge.For other methods ofexpanding your knowledge,see "Learning aboutElectronics" on page 24.(Cover photo courtesy ofTektronix.)

10 How to service Sharp's sweep circuitsBy Homer DavidsonMost service problems originate in the sweep circuit ofcolor TV receivers. By knowing symptoms and cures forthese problems, Davidson focuses on some symptoms andprovides the cures for the supply, horizontal and verticalsweep problems.

24 Learning about electronicsBy Conrad Persson, editorIn today's rapid pace of electronics, keeping up with all ofthe electronics developments is of prime concern for theconsumer. For the service technician, it is just as vital tokeep updated and educated on troubleshooting techniquesand repair methods.

40 Using linear ICsBy Joseph CarrThe author discusses the construction of linear ICs, howthey are used and how to troubleshoot circuits that mightbe defective.

48 Test your electronic knowledgeBy Sam Wilson, ISLET test directorSee how you would do on the Certified ElectronicTechnicians' test. This month's questions cover powersupply.

50 Decibels and time constantsBy Sam Wilson, ISLETThe relationship of logarithms and the number calledepsilon help in explaining the equation for decibels and timeconstants.

52 Symmetrical output circuitsBy Bud Izen, CET/CSMThree basic variations of the complementary type of audiooutput circuit are examined as well as their advantages anddisadvantages in practical applications.

2 Electronic Servicing & Technology November 1983

1

Page 46

Page 22

o in

R2

V+

V-

RS20K

V.

1 °

Departments

4 Editorial

6 Technology

22 Books

26 Feedback

28 Troubleshooting Tips

29 Profax

38 Readers' Exchange

56 Symcure

58 Products

61 Literature

Next month...

One of the more common items we see on the audioservicing bench is the cassette recorder. Although mostrepairs are the garden variety of clean-and-lube routines,occasionally we have to change a head or readjust theinternal controls to get the machine back up to itsoperating potential. Kirk Vistain describes some of theadjustments that most commonly require attention.


EditorialWv

Kill the umpire?One of the problems with athletic events is that

judging is done by mere humans, who are fallible.Even when officials are totally unbiased, theyoccasionally make mistakes. And have you noticedthat when they make a bad call it always goesagainst your team?

In international athletic competition, thedifficulties are compounded by nationalistic fervor.For example, according to researcher Joan deRegt of International Resource Development, anindependent consulting firm in Norwalk, CT,"Political controversies often arise when you havea Yugoslavian judge who awards a Soviet gymnastan undeservedly high score, while an Americanjudge might give that same gymnast anundeservedly low score. With the final outcomes ofthese events often decided by fractions of a point,it's a shame to see prejudice or political hagglingobscure true athletic accomplishment."

How do you eliminate the human factor injudging events such as this? Why, turn it over tothat electronic marvel, the computer, of course. Itwould work something like this. Computerizedimages for the ideal moves for the events would berecorded and made part of a computer database.When the athlete performs in competition, theperformance would be recorded and transformedinto computerized images, which would becompared with the record of the ideal routine. Thescore would be determined on the basis of thiscomparison.

According to de Regt, the use of such a systemis likely to occur "sometime within the next fouror five Olympiads," or roughly by the year 2000.

"It's not such a giant step to take," she says."Many physicians are already using such imagingsystems to analyze the mechanical factors involved

in sports injuries."This conjures up images of what might

eventually be if this type of judging system wereto be exploited to the fullest in all sports.

Just imagine in football, for example. We couldput an electronic device inside the football andinstall sensors in the field. There would be noquestion of whether the offense had made the firstdown, or whether the ball had broken the plane ofthe goal line for a touchdown.

But it's in baseball that electronics could reallydo the job. Wouldn't it be great to eliminate all theumpires? For starters it would be a simple matterto get rid of the guy behind the plate. We'dreplace home plate with a bar-code reading devicelike at the grocery store, and put bar codes on thebaseballs and bats. Not only would you know if theball was in the strike zone, you'd be able to detectwhether the pitch was a fastball, curve, slider orsinker. You could also tell how fast the pitch wasand if the batter swung early, late, high or low, orwhere he met the ball if he made contact. Sensorsalong the foul lines and base paths and at basescould take care of questions of fair or foul andsafe or out.

But then, who would fans have to boo when acall went the wrong way? And who would BillyMartin kick sand on when he got frustrated?Baseball just wouldn't be the same without thosemen in blue whom fans just love to hate.

In this increasingly automated and computerizedworld, some jobs are best left to humans.

9

ELGOTROHiC

Editorial, advertising and circulation cor-respondence should be addressed to: P.O. Box12901, Overland Park, KS 88212.9981 (a suburbof Kansas City, MO); (913) 888-4884.

EDITORIALBill Rhodes, Editorial DirectorNils Conrad Persson, EditorCarl Babcoke, Consumer Servicing ConsultantRhonda Wickham, Managing EditorTina Thorpe, Associate EditorJane Cigard, Associate Editor

ARTKevin Callahan, Art DirectorJoni Harding, Graphic Designer

CIRCULATIONJohn C. Arnst, DirectorEvelyn Rogers, ManagerDee Manses, Reader Correspondent

ADMINISTRATIONR. J. Hancock, PresidentCameron Bishop, PublisherEric Jacobson, Associate Publisher

ADVERTISINGGreg Garrison, National Sales ManagerLiz Turner, Production ManagerRobyn Kahn, Marketing Coordinator

Member, Audit Bureauof Circulation

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ELECTRONIC SERVICING & TECHNOLOGY (USPS 462-050)(with which is combined Electronic Technician/Dealer) ispublished monthly by Intertec Publishing Corp., 9221Ouivira Road, P.O. Box 12901, Overland Park, KS

66212-9981. Second Class Postage paid at Shawnee Mis-sion, KS 66201. Send Form 3579 to P.O. Box 12952.Overland Park, KS 66212-9981.

ELECTRONIC SERVICING & TECHNOLOGY is the "how-to"magazine of electronics. It is edited for electronic profes-sionals and enthusiasts who are Interested In buying,building, Installing and repairing home -entertainment elec-tronic equipment (audio, video, microcomputers, electronicgames, etc.).

SUBSCRIPTION PRICES: one year $15. two years $26,three years $34 in the USA and its possessions. Foreigncountries: one year $20, two years 530, three years $40.Single copy price $2.25; back copies $3.00. Adjustmentnecessitated by subscription termination to single copyrate. Allow 6 to 8 weeks delivery for change of address.Allow 6 to 8 weeks for new subscriptions.

PHOTOCOPY RIGHTS: Permission to photocopy for Internalor personal use is granted by Intertec Publishing Corp. forlibraries and others registered with Copyright ClearanceCenter (CCC), provided the base fee of $2 per copy of arti-cle is paid directly to CCC, 21 Congress St., Salem, MA01970. Special requests should be addressed to CameronBishop, publisher.ISSN 0278-9922

INTERTEC PUBLISHINU CORP.

F1983 All rights reserved.

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Liquid -Crystal technologycolors display capabilities

Tektronix' new color displaysystem does not use shadowmasks or penetration phosphors.Based on a combination of liquid -

crystal and CRT technologies, thesystem combines a monochromeCRT and liquid -crystal "colorswitch" to produce a high -resolution, field -sequential colordisplay.

Because no shadow mask orpatterned phosphors are used,the resolution can be as high asany monochrome CRT. This is aparticular advantage in smalldisplay sizes where high -resolution color has not beenpractical before. Otheradvantages are inherentconvergence (because only oneelectron beam is used), excellentcontrast in high ambient light,and ruggedness, due to theabsence of any fragile shadowmask or complex electron gun.

Previous attempts at producinga field -sequential system havesuffered from the lack of asuitable fast color switch. TheTektronix liquid crystal colordisplay uses a new, proprietary,fast liquid crystal optical switchcombined with a monochromeCRT.

The assembly consists of asandwich of special polarizers andTektronix' proprietary liquidcrystal 7r -cell. The liquid crystalcolor shutter acts similar to a

CH N

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filter that switches between twostates, one allowing primary color#1 to pass and the other passingprimary color #2. The shutterswitches between the two statesin a few milliseconds upon theapplication of a low voltageelectrical drive signal.

The CRT has a simple phosphorwith two separate emission peaksthat are typically, but not limitedto, red and green. The phosphordoes not require any patterningor special process steps. In anyone field, the information writtenon the screen appears only in thecolor selected by the electronicswitch. Each color is repeated ata 60Hz rate, requiring the 2 -fieldsystem to run at a 120Hz rate.This field -sequential system canprovide all possible mixtures of

the two primary colors containedin the phosphor.

Research is continuing toextend the concept to threefields, with three primary colors,which will produce a full colorgamut comparable to or betterthan conventional color displaytechnologies.

Examples of where this newtechnology can provide colorcapability where it has not beenpractical before include: Small instrument displays, such

as oscilloscopes, logic analyzersand spectrum analyzers. In thepast, the need for highresolution to present waveforminformation has been adrawback. Now,Tektronix'liquid crystal color display'sability to function in

both refresh vector andraster display modesmakes new designbreakthroughs possible.

Small process control displays,such as those included onvacuum systems, can nowinclude color for highlightingspecial situations andwarnings.

Computer workstations, wherehigh -resolution is important.

Word-processing equipment,where monochrome displayshave been typically usedbecause high -resolution colordisplays have either not beenpossible or too expensive.Tektronix' liquid crystal colordisplay technology allows theaddition of color without anyresolution penalty. ewe

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How to serviceSharp's sweep circuits

By Homer L. Davidson

In color TV receivers, most ser-vice problems originate in thesweep circuits or the power sup-plies. This certainly is true in 13inand 19in models by Sharp.

These models (Photofact 1959-2,for example) have several dc -

voltage supplies produced by rec-tification of horizontal -sweep pulseor scan peaks. These voltagesources are stabilized by regula-tion of the + 120V that is suppliedto the horizontal -output transistor.However, the situation is com-plicated by two limitations. Atturn -on, no horizontal sweep isgenerated, although it is necessaryfor proper operation of the + 120Vsupply. This same + 120V is essen-tial for proper operation of thehorizontal sweep. These contradic-tions are resolved through a seriesof small steps. An insufficient+ 120V supply at turn -on allowsthe horizontal sweep to operateweakly. The weak sweep increasesthe + 120V actual voltage, whichin turn strengthens the sweep, un-til the sweep is maximum and theregulated voltage is + 120V. Youmust consider this interdepen-dence of horizontal sweep andregulated voltage in troubleshoot-ing of these two basic systems.

Low voltage and regulationFigure 1 shows the complete

low -voltage sources and + 120Vregulation for Sharp model C1935(Photofact 1959-2). In normaloperation of this circuitry, the full+ 164V from the bridge rectifier isapplied to the SCR701 anode.SCR701 is gated into conductionby the I701 power -regulator IC ata time during each horizontal -sweep cycle as required to providea constant + 120V at integratingcapacitor C708. An SCR, once it isgated on, continues conduction un -

on%R702

F701SW7O1 3.32

10W6.

120V

AC

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10000 R709 .01.7-R7135600 2 18K

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R611

8200

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C706 .

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C713 y47µF

+117VSOURCE

w +120VSOURCE

+9.82VSOURCE

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+12.13VSOURCE

3. +18VSOURCE

Figure 1. A bridge rectifier and C706 produce a filtered + 164V supply that isregulated to + 120V by SCR701 and 1701.


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til the anode voltage becomesnegative relative to the cathode.Negative -going horizontal -sweeppulses from the flyback (pins 1 and11) turn off SCR701. Power is ap-plied to C708 from SCR701's rec-tification of these same negative -going pulses as well. Of course, allSCRs can be efficient rectifierswhen supplied with proper gatingand anode/cathode voltages. The+ 164V applied to the SCR701anode changes the zero -voltagepoint of the anode negative -goingpulses. Therefore, most of thepulse height is positive (ratherthan the usual negative) and it isrectified by the SCR701 anode/cathode diode action. C708 in-tegrates these two source voltages(gated dc from the + 164V plusrectified dc from the SCR) into anaverage voltage. When SCR701 isgated -on at the proper time duringeach horizontal cycle, a constantregulated voltage is produced.

It should be clear now why an in-sufficient voltage of about + 76V isobtained from the + 120V supplywhen there is no horizontal sweep:Without the SCR701 anode pulses,one of the power sources is miss-ing, and the regulator gates -on theSCR at incorrect times.

Of course, the + 120V regulatorcannot operate correctly unless itis supplied with + 164V from thebridge diodes that rectify the 60Hzline power. You should verify thepresence of + 164Vdc at theSCR701 anode before you wastetoo much time checking theregulator circuit.

A lower -than -normal supplyvoltage is obtained for thehorizontal -oscillator circuitthrough R611 from the + 120Vsource during start-up (or whenthe horizontal -sweep system isdead). When correct start-up ac-tivates the + 18V source (from rec-tified horizontal -sweep power),D452 is forward biased and theoscillator voltage comes throughR454, producing + 9.82V supplyfor the oscillator. In other words,oscillator supply voltage comesthrough R611 during start-up andthrough R454 during normal runoperation.

Figure 2. Arrows point to important components on the circuit board of a Montgom-ery Ward GSK12981B manufactured by Sharp. Clockwise from upper left, arrows in-dicate SCR701 heat sink, heat sinks for vertical output Q502 and Q503, 1501, 0602horizontal output, and the T602 flyback with focus and screen controls.

VIDEO 16

VERT

SAW FROMYOKE CURRENT

y

1501

SYNC SEPARATORDEFLECTION PROCESSOR

C6011_.0056

R60147

C602+1µF1

HORIZPULSES

2

R606

12K

R607680

R608HORIZHOLD2000

13

R5011200

VERT

DRIVE TOQ501

A

10

C5020.68

+9.82V

R50439K

R503VERT

HOLD100K

+12.13V

HORIZSQUARE WAVES

TO Q601 BASE

Figure 3. Solid-state components for sync separation, horizontal phase detector,horizontal oscillator and vertical oscillator are inside IC 1501.

The de power for the horizontal- source at all times. However, atdriver and horizontal -output tran- turn -on before start-up is com-sistors comes from the + 120V plete, this voltage is less than


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Offer good in USA only and expires 2/29/84. Prices subject to change without notice AD466

QUICKFACTS and PHOTOFACT are trademarks of Howard W Sams & Co., Inc.


+ 80V. The low oscillator, driverand output start-up voltages canproduce only weak sweep, evenwith a non -defective receiver. Ifstart-up is not completed becauseof a sweep defect (or if start-up isfollowed immediately by shut-down), some of these stages mighthave a weak signal plus typicallylow start-up do voltages.

The following are helpful sug-gestions for analyzing supply prob-lems: Loss of horizontal sweep at the

T602 flyback eliminates thehigh voltage, CRT screen vol-tage, CRT focus voltage, + 171Vboost supply, + 12.13V source,+ 18V source and the + 48.7Vsource.

Loss of all + 120V source alsoeliminates the + 117V sourceand the horizontal oscillatorstart-up source voltage.

The + 117V source supplies onlythe sound -output transistors.

The + 171V boost source sup-plies only the red, blue andgreen output transistors thatdrive the CRT cathodes.

The + 120V regulated sourcesupplies the horizontal -outputtransistor directly, the drivertransistor through a droppingresistor, the + 117V sourcethrough a resistor and the oscil-lator start-up voltage throughR611.

The horizontal oscillator oper-ates after start-up from the+ 9.82V source.

The + 12.13V source suppliesthe vertical oscillator, somevideo and chroma stages and theIF stages.

The + 18V source supplies thesound IF stages and somechroma functions. Also, it sup-plies the + 12.13V source(through resistors) and the hori-zontal oscillator start-up volt-age.

Two vertical -output transistorsoperate from the + 48.7Vsource.

Servicing power suppliesHigher -than -normal voltages in

the + 120V source can be causedby leakage in SCR701 or C709

FROM

1501

PIN 4

R6091800 0.001

Q601 HORIZ DRIVER +79VT601

R610 DRIVER

180 +0.41V

C611

+9.82V

R6124700

C6120.001

R6141500

+ 120V

HORIZ

Q602 OUTPUT

R6150.271W

+119.1Vt ANDTOYOKE

1 FLYBACK

C615 00009T602

0.0039

OPENS

Figure 4. The horizontal driver and output stages are not unusual, except for thedamper diode inside the Q602 transistor case and emitter resistor R615, whichsometimes causes a motorboating of the + 120V supply.

(0.0033µF), which feeds a steadycurrent from the + 164V supply tothe + 120V supply. A shortedZD701 zener can maintain SCR701in constant conduction. Also, adefective I701 regulator IC canproduce excessive + 120V sourcevoltages, although this is rare.Another possibility is increasedresistance in R706 (Figure 1).

Most SCR701 leakages can befound with a high -power ohm-meter (low -power mode voltage isnot sufficient to check gate -to -cathode diode action), however theSCR should be removed from thecircuit during the tests. Normalresistance between gate andcathode might measure 500 toperhaps 9000, depending on the

ohmmeter used. Notice, however,that the ohmmeter polarity mustapply the positive probe to thegate and the negative probe to thecathode. Resistances betweenanode and cathode or gate shouldbe very high, perhaps above 5M0.

Low voltage from the + 120Vsupply can be caused by these con-ditions: a low + 164V line -rectifiedsupply voltage, an increasedresistance in R709, decreasedR706 resistance or a loss ofhorizontal sweep.

Always remember that no morethan + 76V can be obtained fromthe + 120V source unless thehorizontal sweep is operating cor-rectly.

Loss of all voltage in both the


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+ 164V and + 120V sources usuallyindicates that a strong overload(such as a shorted horizontal -output transistor) has blown theF701 4A fuse, or opened 3.34R702. A shorted bridge rectifieralso can ruin these two com-ponents, as can a shorted C706main filter capacitor.

Horizontal -sweep problemsI501 deflection -processor IC

(Figure 2, arrow at far right) con-tains the solid-state transistors forthe horizontal and verticaloscillator circuits. A partialschematic is shown in Figure 3.Composite video comes into I501at pin 16. The sync is separated in-side I501 and applied to an internalphase detector. Horizontal pulsesare integrated into sawteeth byR602, C602, C601 and R601.These sawteeth enter I501 at pin 1where they are applied to thehorizontal phase detector.Remember that sync and horizon-tal sawteeth are equally essentialfor solid locking and correct fre-quency. Whenever horizontal fre-quency is unstable, scope thesesignals at pins 16 and 1.

Horizontal -frequency squarewaves exit I501 at pin 4 and areapplied to the Q601 base (Figure 4)as input signal and do positive for-ward bias. Q601 inverts andamplifies the drive signal, and thisstronger signal is coupled andimpedance -matched by T601driver transformer, which in turndrives the base of Q602, thehorizontal -output transistor. Q602then supplies sweep power to thedeflection yoke and the T602flyback.

Notice that the horizontal -output transistor is not a conven-tional type, but it has the damperdiode inside the transistor case. Donot attempt to substitute a com-mon type that does not have thediode. The transistor will fail whenthere is no damper diode. If possi-ble, replace Q602 with the original25D870 or 25D869 component.

All signals of the Figure 3 andFigure 4 circuits can be scopedsafely, which makes the scope theinstrument of choice for testing

R65568

20V PP POS PULSES 8474 D651

FROM T602 op. ,FLYBACKPIN 10 R621

0.47

TO CRT HEATER

ryNC652 I R653

4.7µF Y 10K

+ 17.4V

R652 ZD651

TO 10K OV %1501

PIN 3 C651 + R651lOµFY 15K

Figure 5. Horizontal pulses from the T602 flyback are rectified by 0651, and thepositive voltage is stored in C652. When the pulse amplitude (and the high voltage) isnot excessive, the dc voltage does not exceed the 20V ratings of the ZD651 zenerdiode so no positive voltage passes through R652 to reach 1501 pin 3. When the highvoltage is excessive, voltage passes through ZD651, making pin 3 positive and the IClatches to remove the horizontal -drive square waves. Without drive to the 0601 drivertransistor, the horizontal sweep is killed, and this also removes all scan -rectifiedpower sources, eliminating the picture and sound.

these horizontal stages. Scope thehorizontal signal path startingwith I501 pin 4 and continuing tothe Q601 base, the collector ofQ601, the Q602 base and finallythe Q602 collector. When youlocate the first missing ordistorted waveform, you haveisolated the problem to the circuitstage just prior to that point.

In a number of sets, resistorR614 (Q601 collector voltage,Figure 4) has become open, remov-ing the collector voltage andsignal. A dc -voltage reading ofabout + 9V without any squarewaves at I501 pin 4 usually in-dicates that the IC is defective andshould be replaced. Low do voltagereadings at other I501 pins alsocan point to a defective IC.

Frequently, when a Q602 outputtransistor shorts, emitter resistorR615 burns from the overload.After a new Q602 is installed, theweakened resistor can cause apulsating voltage in all supplies

taken from horizontal -sweeppower.

Horizontal shut -down operationIn theory, any time the high

voltage becomes dangerously high(producing X-rays), an X-ray pro-tection circuit should immediatelyreduce the high voltage to a safevalue. However, none of the late -model color receivers do that. In-stead, the horizontal sweep iseliminated, along with the highvoltage, the raster and the picture.Most circuits maintain this condi-tion until the power is shut off. Ifthe overvoltage condition thattriggered the shut -down is not per-manent, the performance can berestored by turning off thereceiver power for a minute andthen switching it back on. Ofcourse, if the overvoltage condi-tion is still present, the start-upwill be followed instantly by shut-down.

A schematic of the Sharp shut -


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down circuit is shown in Figure 5.Pulses from the flyback windingthat supplies CRT -heater powerare rectified by diode D651, pro-ducing about + 17V to + 18V. C652acts as a peak -reading filtercapacitor and also stores thevoltage for a time to prevent er-ratic operation. Unless the flybackpulses are abnormally high, theC652 do voltage does not goanywhere, because the 20V ratingof zener diode ZD651 is not ex-ceeded. Therefore, the zeneranode and I501 pin 3 have zerovolts, permitting normal oscillatoroperation.

If the flyback -pulse amplitudesincrease abnormally for anyreason (such as an open retrace -tuning capacitor or excessiveregulated voltage), the ZD651zener voltage is exceeded, forcingpositive voltage through ZD651,R652 and I501 pin 3. Thiseliminates the output square wavesat I501 pin 4. Without a drivesignal, the horizontal -sweep circuitstops all operations, whicheliminates raster, picture andsound; the receiver becomes total-ly dead.

A receiver that appears to be inshut -down mode presents severalproblems to technicians. The firstdecision is whether the shut -downaction has occurred because theflyback pulses were excessive (theonly valid reason for shut -down),or whether the shut -down circuititself has a defect that triggersshut -down when no problem existswith excessive high voltage orpulse amplitude.

It is easy to defeat the shut -downcircuit (but this is not recom-mended, as it could result in dam-age to the set). Turn off the ac pow-er, ground pin 3 of I501 and turn onthe ac power. That's all. If thereceiver previously had been inshut -down because of a defect inthe shut -down circuit, the receivernow should operate correctly, in-cluding all supply voltages and thehigh voltage.

If excessive high voltage hadcaused the shut -down, the receivershould operate, but with possibledanger from picture -tube damage

Figure 6. The new T602 flyback is shown mounted on the Sharp chassis, while the oldflyback is at the left. Use only original -type replacements.

before the power can be turnedoff. If you are willing to take thatchance, and the receiver has soundand soon shows a picture, quicklytest for + 120V at the collector(case) of Q602 and then measurethe high voltage. In case bothvoltages are normal, the problemevidently is a defect in the shut-down circuitry. Measure all shut-down components, particularlyD651 and zener ZD651.

A safer method for provingwhether or not shut -down is occur-ring and if it is from excessive highvoltage is to operate the chassisfrom a variable -voltage 60Hztransformer. Start with about 50Vac and slowly increase thevoltage until picture and sound areobtained. Again, slowly increasethe ac voltage and notice if shut-down occurs (and at what linevoltage). A normal receiver shouldwithstand up to almost 130Vbefore the shut -down activates.Shut -down at 90V to 100V hints atexcessive + 120V regulated sup-ply, while shut -down at 100V to110V might be caused by an opencapacitor such as C615 and C620 inFigure 4.

When the + 120V supply voltagecannot be adjusted by R107 to thecorrect voltage, R107 might bedefective. With power off, rotate it

and check the resistance.

No sound, no horizontal sweepWhen the receiver is completely

dead, check the Q602 collectorvoltage. A reading of less than+ 70V hints at a defective bridge -rectified + 164V supply, while a+ 76V or + 78V reading indicatesthe horizontal sweep is notoperating (the low voltage iscaused by the lack of horizontalpulses at the SCR701 anode).

An open Q602 output transistorwith an ohmmeter can have com-plications because of the internaldamper diode. First, a voltage -drop diode tester or a high -powerohmmeter should be used to checkthe transistor out -of -circuit.

When the horizontal -outputtransistor does not have an inter-nal damper diode, the resistancereading between collector andemitter should be high, regardlessof probe polarity. But the damperdiode in Q602 should give a typicalsilicon diode reading when thepositive probe touches the emitterand the negative ohmmeter probetouches the collector. With theprobes reversed, the readingshould be in the megohms. Lowerreadings should arouse suspicionsabout the transistor.

The base/emitter and base/col-


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R515

lector junctions should be checkedwith both polarities in the sameway. Forward -biased junctionsshould show typical resistances forthe meter used, while reverse -biaspolarity should produce resistancereadings approaching infinity.

If Q602 tests normal, but thehorizontal sweep is dead, check allsignificant do voltages followed byscope analysis of any or allwaveforms in the horizontalsystem. These measurements andsome logical thinking locate theproblem area.

Check all connections of theT602 flyback transformer on thecircuit board's bottom side. Poorconnections, particularly pins 1

and 11 for the SCR pulses, havebeen found there. Flybacks mayrequire replacement (Figure 6).

MotorboatingWhen the + 120V regulated sup-

ply voltage varies significantly at aslow rate, causing a motorboatingsound in the speaker and a syn-chronized slow variation of picturewidth, replace resistor R615, theQ602 emitter -to -ground resistor(Figure 4). R615 is likely to needreplacement after Q602 hasshorted and been replaced. Use a0.272, 1W replacement for R615.

Vertical -sweep problemsTransistors for the vertical

oscillator are inside I501. Theseare followed by a driver transistorand two NPN power transistorsthat supply vertical power to theyoke. It is important to note thatthe driver transistor is external tothe IC in Sharp models (Figure7A), while the transistor is insidethe IC in similar models manufac-tured by Sharp for MontgomeryWard and K -Mart (Figure 7B). Pinnumbers for the vertical -hold con-trol and drive -signal output aredifferent for the two versions, asshown.

Scope waveforms can prove thepresence or absence of signal fromI501 on to the yoke, and this isvaluable. However, defects oftendistort the waveforms, makinganalysis difficult. Lack of a drivewaveform at the proper pin (accor-

Q501 DRIVER

VERT

HOLD

1501

DEFLECTION

PROCESSOR

8

VERTHOLD

INTERNALDRIVER

150

TO OUTPUT

Q503

BASE

0. TO OUTPUTQ502

BASE

Figure 7. (A) In Sharp chassis, the vertical driver transistor (0501) is external to 1501,while Montgomery Ward and K -Mart color receivers made by Sharp (B) include thedriver transistor inside 1501. Notice the different pin numbers.

ding to the circuit variations)might indicate a defective I501.Before removing the IC, measurethe supply voltages at the input toR502 (at the vertical -hold con-trol; + 12.13V expected) and atI501 pin 15 (expect + 9.82V). Ifthese two voltages are withintolerance and there is low devoltage and signal level at the out-put pin (pin 2 or 7), I501 should bereplaced.

Output transistors Q502 andQ503 have been known to cause in-termittent height when they openerratically. These intermittenttransistors cannot always be foundby in -circuit or out -of -circuit tests.Therefore, if they are suspected,replace both of them at the sametime. Use the exact replacement,or use ECG373 universal tran-sistors (Figure 8).

Erratic height also can be caused

Figure 8. (Arrows at the top point tovertical -output transistors 0502 and0503. At the bottom, an arrow points toSCR701 on its heat sink.

by corrosion on the vertical hold -control element. Spray the insidewith tuner cleaner and rotate thecontrol several times. If thisreduces the erratic action, youshould replace the control.


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The regulator circuit uses theprinciple pioneered by RCA:Power from the + 164V supplyis released to C708 in timedbursts, with one pulse of do cur-rent during each horizontal cy-cle. This is a practical exampleof time constant at work. C708integrates the do pulses.Heavier loads on the C708 filterrequire the do pulses to bewidened. The I701 circuit deter-mines from the C708 voltagewhen during each horizontal cy-cle the SCR conduction shouldbegin, and a positive pulse is ap-plied to the SCR gate at thattime.

Once started, the current con-duction continues until thenegative -going flyback pulses atthe SCR anode become negativerelative to the de voltage at theSCR cathode. Conductionceases at the same point during

each horizontal cycle. Rectifica-tion of the anode pulses addsvoltage to the + 120V regulatedsupply. Notice that the horizon-tal driver and output transistorsare powered directly from the+ 120V supply, so they areready when the oscillator beginsoperation. During start-up,however, the oscillator receivesa lower voltage from R611, thusforcing the sweep system tooperate weakly. After start-upis finished and the sweep isoperating at full power, theoscillator de supply voltagecomes through D452 and R454from the + 18V supply. Noticethat all de sources (except fouroperating from + 120V) aregenerated by rectification ofhorizontal power. Therefore,these supplies will be dead whenthe horizontal sweep is dead.

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Figure 9. Locations of many components are printed on the bottom of the circuitboard, and wider lines show the general areas for power, vertical and other systems.

One of the first tests when theheight is insufficient involvesmeasuring the de voltages at thetwo vertical output power tran-sistors. If these voltages are low,check 1K51 R513 (brings + 48.7Vsupply to R512 and C504) and 5651R516 that brings supply voltage tothe Q502 collector. When yoke -coupling 470µF C507 is partiallyopen, there will be no height.

Of course, defects in the supplyvoltages can produce height prob-lems. Loss of + 48.7V supply

(Figure 1) might be caused by aleaky D503 that has burned open2251 R520. Replace both if D503 isdefective. Also, remember D503must be suitable for operation at15,734.4Hz horizontal frequency.Do not use a 60Hz top -hat type.

The location of many circuit -board components are marked onthe board's bottom (Figure 9). Inaddition, wide lines show limits ofthe principal areas, such asvertical andpower.

Editor's note: Periodically Elec-tronic Servicing & Technologyfeatures books dealing with sub-jects of interest to our readers.Please direct inquiries andorders to the publishers at theaddress given for each book,rather than to us.

Electronic Miniatures-ABuyer's Guide, by S.E. Harris;Tab Books; 304 pages;$17.95 hardbound, $12.95paperback.

This guide book tells what is onthe market in miniature electronicgadgetry - cameras and taperecorders, electronic games,medical devices, computers,radios, televisions and more. Thebook covers the evolution of elec-tronic miniatures, microelec-tronics, repair of microelectroniccircuits, miniature television cir-cuits, cassette recorders,miniature entertainment systems,miniature broadcast receivers,calculators, pocket computers,clocks and watches, micropro-cessors and assorted miniaturegadgets.

Also included are electronic drillpresses, personal smoke alarms,blood pressure/pulse monitors,radar detectors and a sportsforecasting kit.Published by Tab Books, Blue Ridge Summit,PA 17214.

Fundamentals of StereoServicing, by Joel Goldberg;Prentice Hall, Inc.; 299 pages;$22.95.

This working handbook coversstereo repair and troubleshootingtechniques and includes blockdiagrams, schematics and in-depthcircuit coverage. Guidelines aregiven for complete professionalservicing of transformers, rectifiersystems, bridge output systems,low-level amplifiers, AM and FMtuners, matrix decoders, switchingdecoders, cassette systems, car-tridge systems, reel-to-reelsystems, and discrete and IC cir-cuits. The handbook gives profes-sional safety precautions, step -by -


step troubleshooting methods andhow -tos for using test equipment.

The book shows how to identifyinput and output connections foreach type of amplifier circuit, an-ticipate the approximate size andshape of input and outputwaveforms, pinpoint how inputand output transducers help toproduce a signal voltage and deter-mine which type of tuner developsthe audio signal from themodulated RF signal beingtransmitted.Published by Prentice -Hall, Inc., EnglewoodCliffs, NJ 07632.

The Video Guide, by CharlesBensinger; Howard W. Sams &Company; 255 pages; $18.95.

This survey of current videoequipment, trends, techniques andprograms provides the reader witha general overview of the video in-dustry today. Topics includecameras, VTRs, videotapemonitors, projectors, video-cassette systems, the video por-tapak, ENG systems, main-tenance, troubleshooting and pur-chasing equipment.Published by Howard W. Sams & Company,4300 W. 62nd St., Indianapolis, IN 46268.

Concepts of Digital Electronics,by Harry M. Hawkins; TabBooks; 196 pages;$17.95 hardbound, $11.95paperback.

This book shows how anyone canunderstand and use low-cost 7400series integrated circuits to pro-duce working digital devices in-cluding a power supply and abreadboard experimenter. Writtenin an easy -to -follow -and -under-stand style, the book shows howclocks, flip-flops, shift registers,logic gates and other digitaldevices function and explains howto use them in a variety of prac-tical applications.

Several digital electronics con-cepts are introduced including thedifferent number systems - binary,decimal, octal and hexadecimal.BCD, Baudot and ASCII codes andfundamental digital operations in-cluding AND, NAND, OR, NORand Exclusive OR are covered.The author has included hands-oninformation on the basic principlesof digital electronics experimenta-tion and how -tos for troubleshoot-ing digital circuits.Published by Tab Books, Blue Ridge Summit,PA 17214.

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Learning aboutelectronicsBy Conrad Persson, editor

The rapid pace of the electronics"revolution" has been muchcelebrated in the press, on televi-sion and in general conversation.Its effect on the lives of all of ushas been profound. To many itmeans improved communications,expanded entertainment choicesor electronic help in calculatingand computing. To others it meansa threat of unemployment as com-puters and robots perform moreand more routine tasks.

To yet others, servicing techni-cians and electronic enthusiastsfor example, it means stillmore to learn about electronictheory, practical applications ofelectronics and servicing, andrepair of electronic products.Whether learning about this newelectronic . technology is an in-tellectual challenge or a drudgedepends upon an individual's at-titude, and of course whether ornot he simply wishes to study or ifhe is obliged to study. Whateverthe case, there is plenty of newmaterial to study in electronicswith more generated every day.

Several avenuesThere are two pivotal decisions

to be made when you're decidingabout further education: What,precisely, do you need to learn andhow will you learn it?

It's important to do a thoroughanalysis of exactly what it is youwant to learn. I occasionally hearsomeone say, "I want to learnabout computers," or somethingequally vague. The question thatneeds to be answered is, "What doyou want to learn about com-puters?" The answer might besomething like, "I want to take anintroductory course in computersso I can understand the jargon andknow how hardware and softwareinterrelate, so that I can knowwhat further courses to take to

learn servicing." That doesn't pinit down completely, but it doesstate some specific goals.

Once the specific goals are set,the next consideration becomeshow to achieve them. One simplebut effective method might be tocontact other technicians in yourarea. If you have a skill that theylack and vice -versa, why not ar-range for a session in which youeducate each other.

Self studyAnother simple but less effective

method is to buy a book on the sub-ject and study it yourself. Depend-ing upon a number of factors, in-cluding the complexity of the sub-ject, the quality of the book, andyour own self discipline, this ex-perience might bring anythingfrom complete understanding tofruitlessness. Home -study coursesoffer a major improvement overstudying from books. The materialis broken down into study units,someone tells you what is expectedof you, and you get feedbackthrough regular tests.

Schools and seminarsIf time and money permit, a

more effective way to learn isthrough structured class and labcourses. Here again there aremany avenues. Public and privatetechnical schools throughout thecountry offer a selection of coursesfrom the most elementary in-troductory courses to detailedtheory and design. If you have thetime and the budget to travel,manufacturers of home electronicequipment offer to servicingtechnicians seminars on the opera-tion and servicing of specificitems.

Identifying theavailable resources

A local school may have just thecourse you need listed in itscatalog. One of the book publishers

might have just the book or seriesof books to fill in the gaps in yourknowledge. One of the associationsrelated to home electronics equip-ment manufacturing sales or ser-vice may have just the item of in-formation you need or be able topoint you in the right direction.

The following text lists a numberof correspondence schools, bookpublishers and associations whomyou might want to contact for fur-ther information on what educa-tional opportunities they have tooffer.

Trade associationsElectronic Industries

Association (EIA)Consumer Electronics Group2001 Eye St., N.W.Washington, DC202-457-4919

Electronic RepresentativesAssociation (ERA)

20 East Huron StreetChicago, IL 60611312-649-1333

Electronic TechniciansAssociation (ETA)

RR3, Box 564Greencastle, IN 46135

National Association of Television& Electronic Servicers ofAmerica (NATE SA)

5930 S. Pulaski RoadChicago, IL 60629312-582-6350

National Association of RetailDealers of America (NARDA)

2 North Riverside PlazaChicago, IL 60606312-454-0944

National Association of RecordingMerchandisers (NARM)

1060 Kings Highway NorthSuite 200Cherry Hill, NJ 08034609-795-5555


The new AWS DM -3010. It's not just another DMM.It's a complete electrical/electronic testing system.

DM -3010

41DIGITAL MULTIMETER SJA-870 JAW ADAPTOR

43HFE-840 TEST ADAPTER

95

/5HVP-860 HIGH VOLT PROBE

95,099'

__ . _ ,.,...:. TTkS

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i

o.....n'.t

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w cc..

Today's electrical and electronictesting requirements call forequipment that can handle a widerange of applications. That's why nowmore than ever you need the new AWSDM -3010 Testing System.

To start off with, the DM -3010 DigitalMultimeter has an unbelievable $80price tag. It offers 34 ranges with push-button control plus features usuallyfound in much more expensive modelssuch as: 10 Amp AC/DC range; UL1244type test leads; overload protection onall ranges; Hi and Low power ohms inall resistance ranges and more.

Complete the system by simply addingthe following accessories as you needthem...SJA-870 Snap -Around Jaw Adaptor.Reads 0-1200 Amps AC. Its large jawsfit easily around any conductor up to2-15/16" in diameter.HFE-840 Test Adapter. If your workrequires transistor and diode testing,this pocket-size adapter is a must.HVP-860 High Voltage Probe. Providessafe, easy and reliable readings of 0-501CVDC on low power high impedancecircuits.

So compare the DM -3010 TestingSystem for yourself. You'll find that noother company offers a comparablesystem at these low prices.

For more information on the AWSDM -3010 Testing System, see your localdistributor today or contact A.W. SperryInstruments Inc., P.O. Box 9300,Smithtown, N.Y. 11787. Call Toll -Free800-645-5398 (N.Y., Hawaii, Alaska callcollect 516-231-7050).

A.W. SPERRYINSTRUMENTS INC.

National Electronic DistributorsAssociation (NEDA)

1420 Renaissance DrivePark Ridge, IL 60068312-298-9747

National Electronic ServiceDealers Association (NESDA)

2708 W. Berry St.Ft. Worth, Texas 76109817-921-9061

Recording Industry Association ofAmerica, Inc. (RIAA)

888 Seventh Ave.New York, NY 10106212-765-4330

Technical book publishersHayden Book CompanyRochelle Park, NJ 07662

McGraw-Hill Book Company1221 Avenue of the AmericasNew York, NY 10020

Prentice -HallEnglewood Cliffs, NJ 07632


Howard W. Sams & Company4300 W. 62nd St.P.O. Box 558Indianapolis, IN 46206

Tab BooksBlue Ridge Summit, PA 17214

Van Nostrand Reinhold Company135 W. 50th St.New York, NY 10020

Home studyCleveland Institute of

Electronics1776 E. 17th St.Cleveland, OH 44114

Cook's Institute of ElectronicsEngineering

Desk 15P.O. Box 20345Jackson, MS 39209

Electronic Institute of Brooklyn4823 Avenue NBrooklyn, NY 11234

Grantham College of Engineering2500 S. La Cienega Blvd.Los Angeles, CA 90034

Heath CompanyBenton Harbor, MI 49022

National Institute of Technology1701 W. Euless Blvd.Euless, TX 76039

National Technical Schools456 W. Santa Barbara Ave.Los Angeles, CA 90037

NRI Training for ProfessionalsMcGraw-Hill Continuing

Education Center3939 Wisconsin Ave.Washington, DC 20016

Trade schoolsNational Association of Trade and

Technical Schools2021 K Street, N.W.Washington, DC 20006


INTRODUCING

THEPROTECTOR

6000"TOTAL PROTECTION FOR YOUR

SENSITIVE ELECTRONIC EQUIPMENT.Something that you can't even see may be slowlybut surely killing your expensive electronic equip-ment. It's transient voltage, and it can be fatal tocomputers, medical equipment, electronic games,videotape recorders, electronic test equipment,electronic cash registers - almost any of today'ssophisticated solid state equipment.

THE TRANSIENT VOLTAGE PROBLEM.Most of this modern electronic equipment usesLSI and MOS semiconductor devices which areextremely sensitive to voltage transient surges or"glitches." In fact, a large percentage of equip-ment failures can be directly linked to the damag-ing effects of over -voltage line transients tounprotected, highly fragile components.

THE PROTECTOR 6000'" SOLUTION.Not to be confused with other transient voltageprotection units available today, THE PROTECTOR6000 uses state-of-the-art solid state componentsand exclusive circuitry to provide you with com-plete and total protection from transient voltagesurges of up to 6,000 volts. THE PROTECTOR6000 uses silicon PN junction devices - provento provide the fastest response to surges! Theyhave a statistical life expectancy of over 20 years.THE PROTECTOR 6000 has a maximum clampingvoltage of only 335 volts, well below the voltagerating of other transient protection devices whichcommonly use much less effective MOV's or gasdischarge tubes. It also provides full protectionfrom electro -magnetic and radio frequency inter-ference. The unit operates in both common anddifferential modes, and is outfitted with a circuitbreaker to guard against severe current overloadsover 15 amps.

Why take chances with your expensive electronicequipment? For full details contact your localNTE distributor or write:

NEW -TONE ELECTRONICS, INC.44 Farrand St., Bloomfield, NJ 07003

THE PEOPLE WHO BRING YOU THE TCGLINE OF SEMICONDUCTORS.

1983 New -Tone Electronics. Inc.

Leakage testingIn response to the letter in June

1983 Feedback, I would like to addone item. Our shop does manyrepairs on line -operated musician'sequipment. It is common to findsome sort of capacitor from 0.05 to0.3µF from one side of the line tothe chassis, with both 2- and 3 -wireline plugs right from the factory.The 2 -wire types are common inolder units, and you may find aswitch to allow the hot side of thecapacitor to be to either line side.The result is that:

a. To properly measure leak-age, you must be sure that ifa third (neutral) is used it isoperational.

b. You will probably have tocheck both (or all 3) switchpositions, and you may haveto repeat this with the linecord in the case of a 2 -con-ductor plug.

c. A value of 0.05µF allowsabout 2mA of ac 60Hz toflow, far in excess of the typ-ically allowed 0.5mA of ac.Therefore, the older unitsmay not pass today's leakagetest, and no leakage specs ex-ist on them anyway.

I highly recommend that anyshop that sees a piece of line -

operated musician's equipment notlet one out of the shop without ask-ing the customer about installing a3 -wire line and plug. Musicians areused to receiving shocks fromequipment, but the liability situa-tion is questionable. I make themsign a waiver. And no, you cannotremove the capacitor, because themusician may complain he cannotget rid of the "hum" problem.R. FleischerSouth Lake Tahoe, CA

Capacitor cautionsI have just read Mr. Honey's ar-

ticle on capacitors ("SpecialCapacitors for Television, May1983 ES&T) and did enjoy hisknowledge of them, and found thearticle interesting and infor-mative. I found myself driven to

write to you about a serious bit ofadvice that he gives concerningthe 4 -legged capacitor used inmany horizontal output stages.

He says "I prefer the separatecapacitors instead of one large onefor retrace use...I do not normallyreplace the 22-5001 capacitors(Zenith part number) capacitorswith a 4 -legged one...I replace theoriginal part, usually with a betterquality replacement...The reasonsI prefer separate capacitors aresimple. First, one large capacitor(4 -legged or not) holds more heatinternally and can acceleratefailure."

While he is basically correct inhis assumptions, his advice is total-ly incorrect and could bringlawsuits to anyone following it.The federal government has man-dated that parts within criticalareas are not to be modified in anyway. Replacement of the 4 -leggedcapacitor with several singlecapacitors is definitely modifyingthe circuit and makes you respon-sible for what you have done.

His knowledge of the circuit orhis encouraged modification of it iswrong because of the legality ofit-not the performance of the cir-cuit. I do agree with his circuitlogic but know your magazine orany other cannot support the ad-vice he has given.George Savage, CETDoniphan, NE

Honey's replyI believe Mr. Savage has

misinterpreted my article, orperhaps I didn't express mythoughts clearly.

At no time have I advocatedmodifying "critical areas" withsubstandard parts. I also never im-plied that I replaced the 4 -leggedcapacitor with several singlecapacitors, even though such amod would be safer and morereliable.

I did suggest that "better thanoriginal parts be used" and thateven when the manufacturer sup-plied a mod kit consisting of a4 -legged capacitor, I didn't use it.A circuit can be "redesigned" orrepaired in any way I see fit, aslong as safety factors are main-tained or improved.

The replacement parts I sug-gested in all cases were betterthan the original. The whole point


of the article was to supply enoughinformation so that anyone coulddetermine what type of capacitorwould make an adequate replace-ment.

No law exists that says that"only the manufacturers originalparts or part numbers must beused in repairing television sets."Anything can be used as long as itis equal to or better than theoriginal OEM part.

Incidentally, a good way to testthe 22-5001 Zenith capacitors tosee if one or more are open, is tocut one loose while monitoring thehigh voltage (be sure set is offwhile cutting). If no voltagechange is apparent when the set isturned on again, the capacitor isopen. If the voltage changes 1 to2kV, the capacitor was probablygood. Replace the lead and con-tinue. In this way, the bad onescan be weeded out a little faster ifproper test equipment is notavailable.C. A. HoneyOntario, CA OW,

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One more thing. Kit prices are lower thanthe total cost of the individual parts. So seeyour RCA distributor today. Also ask for acopy of the VCR Parts Cross Reference ofmore than 8000 VCR parts (Form1 F6627) and VCR Tool Catalog (Form1F6857). Or write: RCA Distributor andSpecial Products Division, 2000 ClementsBridge Road, Deptford, NJ 08096.

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TroubleshootingTips

No sound and no pictureSony KV -1711 chassis SCC-63A(Photofact 1503-1 or 1625-2)

A customer who brought the Sony TV receiver tome explained that another shop had given up tryingto repair it after six weeks. They had installedseveral F602 4A line fuses, an unidentified elec-trolytic capacitor and the D517 damper diode.

Usually, I carefully check all previous repairs,because mistakes often kept the previous technicianfrom completing the repair. Unfortunately, I forgotto check this time.

A resistance check of the regulated + 130V supplyshowed a 260 short to ground, which is sufficient toblow the line fuse. Rapid in -circuit tests of thebridge rectifiers and all transistors on the power -

supply board did not locate any defects. I discon-nected the wires from the audio -output and thehorizontal -sweep circuits, and the short was gonefrom the + 130V supply. Additional tests proved theshort was in the horizontal circuit, so I reconnectedthe audio wire, leaving the horizontal wire discon-nected. When 120V power was applied, the fuse didnot blow, but R617 in the power supply began smok-ing from overload. I put aside the R617 questiontil later.

I tested all horizontal diodes and transistors by thevoltage -drop function of my DMM, but none ap-peared to be bad. I tested the yoke, flyback andother components by resistance measurements, butfound no defects. The 260 short remained as I un-soldered each flyback pin in turn until pin 10 of T501was disconnected, eliminating the short. The + 130Vfor the Q510 horizontal -output devices comesthrough R904 (100) to pin 10. Next, I noticed a

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jumper on the yoke plug that (when the plug isremoved) opens the circuit between Q510 and T801,the high -voltage transformer. By opening thejumper, I proved the short was on the T801 leg ofthe wiring. The wire went back to the power -supplyboard, which held L601, L602 and C608. I wasrelieved to measure a 140 short in C608 (0.024µF1000V) that coupled sweep power to the T801primary. The primary low end is connected to thecathode of Q510 which is grounded through a 1.80resistor. Therefore, C608 was responsible for theoverloaded + 130V supply.

After I replaced C608 and restored all connec-tions, the short was gone, so I switched on the 120V



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INschem

tlicr

This schem

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technicians only. This instrum

ent contains nouser -serviceable parts.

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1983

The other portion of this schem

atic is found onthe other page of this P

rof ax section.

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RT

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RIZ

. (DC

MO

DE

)!

U Integrated circuits and m

any otherM

mleo ductors are electrostatically sem

i -live and therefore require the ~

al han-dling techniques described under"E

lectrostatically Sensitise (E

S) D

evice*"In the Servicing Precautions

section ofbest w

ills data.

Product safety should be considered w

hen component replacem

ent ism

ade in any areas of a receiver. The shaded areas of the schem

aticdiagram

designate the components in w

hich safetyis of special

significance. It is recomm

ended that only exact cataloged parts be usedfor replacem

ent of these components.

Use of substitute replacem

ent parts that do not have the same safety

characteristics as recomm

ended in factory service information m

aycreate shock, fire, excessive x-radiation or other hazards.

Reprinted from

RC

A S

ervice Data F

ile 1983 KC

S 204.

Copyright 1983 by perm

ission of RC

A C

onsumer E

lectronics.C

opyright 1983, Electronic S

ervicing & T

echnology, P.O

. Box 12901, O

verland Park, K

S 66212.

Cau

tion:

A s

epar

ate

isol

a-tio

n tr

ansf

orm

er m

ust b

eus

ed w

hen

serv

icin

g th

isch

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s.

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er -

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duct

saf

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ld b

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nsid

ered

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n co

mpo

nent

rep

lace

men

t is

mad

e in

any

are

as o

f a r

ecei

ver.

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sha

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sche

mat

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m d

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nate

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com

pone

nts

in w

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saf

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spe

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nly

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alog

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arts

be

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itute

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lace

men

t par

ts th

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o no

t hav

e th

e sa

me

safe

tych

arac

teris

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as r

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men

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in fa

ctor

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rvic

e in

form

atio

n m

aycr

eate

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ire, e

xces

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adia

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66212.

power; F602 blew instantly. Then I remembered theD517 damper diode had been replaced by theprevious technician. The soldering of D517 appearedto be satisfactory. I decided to re -install the olddamper diode, because it tested fine externally andnot all replacement parts will operate correctly inSony machines. After one end of the new damperwas unsoldered, I noticed the polarity was reversed.Of course, this connected its anode to the B+through the flyback, producing a short when thevoltage was higher than 0.7V. I re -installed the olddamper diode.

When the receiver power was applied next time,the sound had a loud hum and the picture showedtwo wide black bars. I installed a new R617 (which Ihad forgotten to do earlier) and measured + 158V atthe + 130V regulated supply. Junction tests of allregulator transistors revealed Q601 had an openbase -to -collector junction and Q602 was shorted be-tween emitter and collector. After these transistorswere replaced and the regulated voltage adjustedfor + 130V, the receiver operated normally.

This case illustrates some of the complicationsfrom two separate defects, and the dangers of notchecking all previous repairs for mistakes.

Phillip M. JonesMartinsville, VA

Poor focusAdmiral 19C8248L(Photofact 1766-1)

A blurred picture and lack of visible scanning linesindicated a problem with focusing. When I openedthe receiver, I found that someone had butcheredthe focus -divider network, evidently in a misguidedattempt at forcing the circuit to give better focus. Iinstalled a new network, but this did not improvethe focus. At CRT socket pin 9, the focusing voltagetested below 1kV, far below the expected 5kV.

High voltage at the CRT anode was satisfactory.A check of the focus control showed someroughness, so I installed a replacement component.Again, there was no improvement.

The focus voltage at the tripler measured aboutright. When I disconnected the wire to CRT -socketpin 9, the voltage at the wire jumped up to almost5kV. This made me suspect that excessive picture -tube current was loading down the focus voltage.The CRT tested normal on a CRT tester.

I removed the socket from the CRT base andtested for leakage between pin 9 and all other socketpins. I found no leakage. I repeated all the previoustests and examined the schematic carefully, butwithout success.

Finally, I remembered that the only componentnot tested completely was the picture -tube socket.After I dismantled it, I noticed that the spark gapdidn't look right, although it didn't test shorted. Indesperation, I installed a new socket, and this curedthe focus problem.

Although no arcing had been seen or heard, it wasclear that the spark gap had been breaking downunder the focus voltage. This is one lesson I willremember for a long time.

Mike B. DanishAberdeen Proving Ground, MD

"If it§ not a GE, I thinkI'll just stay in the truck."

In this business, you never know what you'llrun into. So it's always nice to run into a GEcolorTV, packed with its own Mini -Manual,including a schematic, parts list and trouble-shooting guide. Since 1977 we've put a Mini -Manual inside every color set we make. Lookfor it every time that you're servicing a GEcolor TV. And use our toll -free numbers forparts orders and technical assistance. You'llhave a good reception the next time yourGE customer needs service.

MINI -MANUALSERVICE INFORMATION

FOR TECHNICIANUSE ONLY

CCESSIBLE FROM INSIDETV SET ONLY

We bring good things to life.

GENERAL ELECTRIC


For sale: Sencore VA48, mint condition, with manual and probes, $800.Rnhe'rt L. Blount, 40 S.W. 8th Ave., Delray Beach, FL 88444.

Readers' Exchange

For sale: Electronic Servicing, 1968-1980, $50 plus shipping; Sams38-700, $400 plus shipping; B&K 1076 TV analyst, $175. Paul S. Funk, 607E. Cherry'Lane, Souderton, PA 18964; 215-723-2355.

For sale: FM stereo pack, model CU-951UA with service manual, forPanasonic car radio, $15. Al Crispo, 3225 Chipmunk Drive, New PartRichey, FL 33552.

Needed: IC for Philco television, #IC5/46-5002-5, or MotorolaHEPC6077P. Wizard Electronics, Rt. 5, Box 522, Renick, WV 24966;304-497-2066.

Needed: Electronic Measurements Corporation (EMC) constructionmanual for model 801 comparator bridge and in -circuit capacity checker.Send photocopy or original COD. Max Emerson, 1923 N. Texas, Weslaco,TX 78596; 512-968-3913.

Needed: Service manual (in English) for NordMende Electronics (German)KM -394 distortion analyzer; working NordMende SRG389 sine/squaregenerator; parts/service manual for Sansui SD -7000 R -R tape deck (1971).Steve Bender, Bengrun Research Labs, Box 28360, Queens Village, NY11428; 212-776-2909.

Needed: Simpson 498 field -strength meter, VHF -UHF tube type, andHickok model 235A field -strength meter, VHF -UHF tube type. Batteriesnot needed; ok if inoperative. Jim Shoemaker, 600 First St., Leechburg, PA15656; 412-842-8321.

Needed: High -voltage cup and socket for Panasonic color television, modelCT -21P. State price. George Saylor, 2319 Parrish St., Philadelphia, PA19130.

Needed: Service manual/schematic for model 1700, 115V, 60CPS, 21WMagnus organ. Will pay reasonable price. Wilk& Radio & Electric, 6056Steubenville Road, SE, Amsterdam, OH 43903.

Needed: Up-to-date tube layout charts for Mercury model 300 tube testeror address of company. Earl P. Anderson, 1828 W. Jewell Ave., Milwaukee,WI 53221.

Needed: Schematic diagram and power transfórmer for Marquette engineanalyzer, model 40-175. Ed Peterson, 751 Jakway, Benton' Harbor, MI49022.

Needed: Sencore VA48, Sencore TF46 and Sencore UPS164. Rod Wells,4528 N. Dearing St., Fresno, CA 93726; 209-291-5071.

Needed: Adapter cables for Sylvania Check -a -Color CK 1500X rig,transverter, matching cords and other updating equipment. A. Johnston'sElectronics, 14 Waldwick Court, Toms River, NJ 08757.

Needed: Sencore LC53 Nate Lilienthal, 29515 Quailwood Drive, PalosVerdes, CA 90274; 213-377-9913.

Needed: Power transformer for Hewlett-Packard model 130A scope; P/N910-148 replaced by P/N 9100-0078. Dewey Landis, 2712 Mayfair N., Seat-tle, WA 98109; 206-282-2624.

Needed: Service manual or schematic for Sears b&w television, model5025, chassis 562.10453, 110Vac and 12Vdc, and same for Candle b&wtelevision, model MT510 or MT510A, 110Vac and 12Vdc. John R. An-drade, Rt. 1, Box 40, San Gregorio, CA 94074.

Needed: IC ECG 782 and picture tube 370 AUB22 for Philco 13in colortelevision. J. Rosenblatt, 2063 E. 56 St., Brooklyn, NY 11234.

Needed: Parts or a complete Hallicrafter model SX-62 receiver. PaulCapito, 637 W. 21 St., Erie, PA 16502.

Needed: Service manual and operator's manual for HyGain VHF marinetransceiver, model 655. Mark Moorman, P.O. Box 2923, Greenville, NC27834.

Needed: Tekfax volumes 101-105 and Supremes TV volumes 1-4, and 11.C. T. Huth, 146 Schonhardt St., Tiffin, OH 44883.

Needed: Instruction manual and schematic for Robyn CB transceivertester, model MT -701. Will buy or copy and return. Hubert McGraw, 10136Renfrew Drive, El Paso, TX 79925.

Needed: Sencore LC -53 Z -meter and Sencore VA48 analyzer. Both mustbe in A-1 condition. David A. Tabor, Box 56, Killdeer, ND 58640;701-764-5017.

Needed: Schematic for Columbian Hydrosonics Aqua Probe, modelCH -363. Will buy or copy and return. Robert A. Ports, 1420 Appian Drive,Punta Gorda, FL 33950.

For sale: Heathkit VTVM model 1M-5228. Includes probes, manual andextra 50kV probe; new and accurate; asking half of kit price. C. Gil/ow,P.O. Box 177, Springer, NM 87747; 505-483-2363.

For sale: 1600 Sams Photofact folders from 1 to 1850, $15. Don's TV, 119Lisann St., Tallmadge, OH 44278.

For sale: Sencore VA48 analyzer; used less than 20 hours; $850. Ron Car-ron, Box 365, Highland, KS 66035; 913-442-3255.

For sale: New and used TV tubes, many boxed; 30 cents each plus $1.50postage. Send stamped envelope for list. Will buy or trade for TV solid-state troubleshooting flow charts and books. R. Stanley, 428 W. RooseveltBlvd., Philadelphia, PA 19120.

For sale: Two B&K 415 sweep/marker generators; one new, $250, oneused, $100. Jim Moyer, 417 E. Elm St., Tamaqua, PA 18252; 717-668-2607.

For sale: Sencore VA48 analyzer and Sencore RC167 substitution boxR/C. Both units, with manuals, $800. Raoul Vazquez, 7251 S.W. 9 St.,Miami, FL 33144; 305-264-6785.

For sale: Sencore VA48 video analyzer, $825, manuals and probe included.Excellent condition; price includes shipping. George Lazoryszak, George'sTV, 4432 N. Chadwick St., Philadelphia, PA 19140.

For sale: TV parts and equipment at good discounts. Send SASE. MarvinWarmbrand, 8 Dusk Drive, Centereach, NY 11720.

For sale: Avantek 120 -degree LNA, $375, and Sa-TEC R2B receiver,$375. WSEP, Sparta, WI, 608-269-2392.

For sale: RCA junior volt ohmist with probes and service manual, $50;high -voltage probe, $15. Al Crispo, 3225 Chipmunk Drive, New PortRichey, FL 33552.

For sale: Sencore CR143 CRT tube tester, $125; Anders CM -100capacitance meter, $60, used less than two hours. Buyer pays UPSpostage. Walter Fiscus, Audio Repair Service, Route 1, Box 345, Oxford,NC 27565; 919-693-1066.

For sale: Jackson model 523 oscillograph and Jackson model 420 universaloscillator, manuals included. Manufactured in 1937 by the Jackson Elec-trical Instrument Company, Dayton, OH. These instruments are operable.J. L. Carter, Box 464, Hooker, OK 73945; 405-652-2049.

For sale: Sencore CB41 and CB42 CB analyzer in like -new condition. In-cludes manuals and test leads; $525 or best offer. Martin Major, 15810 Sap-wood St., Tampa, FL 33624; 813-961-7303.

For sale: Sencore TF46 Super Cricket transistor FET tester, new, $145;B&K model 466 picture tube tester rejuvenator, used only on service calls,$65; Conar model 311 resistor capacitor tester, $25. All with manuals.Paul's TV, 260 Main Cross, Charlestown, IN 47111; 812-256-3119.

For sale: EICO model 145 multisignal tracer, $75; EICO model 944flyback/yoke tester; Precision Tube master series 10-2 tube and batterytester, wood dovetail box, antique, $150. Ed Barlow, Box 29, Tweed, On-tario, Canada KOK 3J0.

For sale: Hewlett Packard model HP608D signal generator, $220; B&Kmodel 2040 CB generator, $185; RCA 10J106 TV test jig, with cables,$215. Jeffrey Jeffers, 337 Lambert Ave., Groveport, OH 43125; 614-836-5368.

For sale: B&K model 1077B TV analyst, $300; B&K model 467 CRTrestorer and tester, $300; Triplett 5in VTVM, $75. J. L. Bachelor, 2538Tam O'Shanter Drive, Cleveland, TN 37311; 615-472-8726.

For sale: B&K 1077B TV analyst, $200; B&K 415 solid-state sweep/marker generator, $200. Both like -new condition; manuals andleads/probes included. Tom's TV & Sound Service, 412 Grand Mesa Ave.,Grand Junction, CA 81503; 303-243-1324.

For sale: Heathkit model 1GB-1023 RF signal generator, $35; Heathkitmodel 10-101 vector scope, with manuals, hardly used, $65. Both for $100plus shipping. Don Kerkhoff, 1266 Vermont St., Quincy, IL 62301.

For sale: B&K 1077B analyst, used only three times, $350. H. Solano, P.O.Box 1074, Bricktown, NJ 08723.


For sale: 85 books on radio and television and some on video; mostly hard-back, all in excellent condition; $200 for all. Daniel Seidler, 5827 S. Camp-bell Ave., Chicago, IL 60629.

For sale: Hickok model 536 vacuum tube tester; Hickok model 209AVTVM; and Hickok model 675A oscilloscope. All probes and manuals in-cluded. Edward H. Frazier, R. R. #2, Box 632, Brownsville, TX 78520.

For sale: Sencore SC60 scope, $1150; Sencore CA55 capacitor analyzer,$275; and Leader LDM851 multimeter, $65. Val Obal, 3201 S. 73 St.,Omaha, NE 68124.

For sale: Sencore LC53 Z -meter, like new; B&K model 1477 dual -trace,trigger -sweep oscilloscope, like new; Bell & Howell complete 16 -volume TVcourse with or without hardware. Best offer for one or all; write for com-plete list. Rod Wells, 4528 N. Dearing St., Fresno, CA 93726; 209-291-5071.

For sale: Hundreds of old radio and TV tubes (boxed) for $1 each pluspostage. Also old issues of Radio News, Electronic World, Radio Craft,Audio Craft, PF Reporter, Electronic Servicing, Radio Electronics, etc., $2a copy plus postage; special price for whole lot. J. R. Blundin, 151 W. 3 St.,Mt. Carmel, PA 17851; 717-339-0402.

For sale: Hammarlund SP -600 receiver, B&K model 470 CRT tester, andtwo teletypewriters. W. A. Frederickson, 3103 W. 12 Ave. Ct., Broomfield,CO 80020.

For sale: Tektronix model 212 scope, portable ac/NiCads, $600 or best of-fer; B&K 1476 scope, LN, with probes, $300 or best offer; and Wavetechmodel VCG116 function generator, general purpose, $400 or best offer. Allworking and with manuals; COD/UPS. A&B Electric Company, 1883 E.Main, Rochester, NY 14609; 716-288-1520.

For sale: Six like -new Admiral 3M2D chassis, $25 each; set of six DK36CW6 and 6LU8 tubes, $750. Jenkins Service, 9 Airlene, Bridgeton, MO63044.

For sale: Sams CB Photofacts in intermittent sequence 1 through 257 (125volumes). $250 plus shipping. Richard E. Wood, Box 338, Lenn Road,Newburgh, IN 47630.

Wanted: Good, used b&w CRT 16VDGP4 and Zenith flyback 95-3332-01.Miscellaneous recent Sams Photofacts for sale. M. B. Danish, P.O. Box 217,Aberdeen Proving Ground, MD 21005.

Needed: Schematic for a Panasonic AM/FM stereo receiver (model RE8126). Inform me of your terms. Thomas Lutz, Consumer Electronics, 614Edwards St., Aurora, IL 60505.

Needed: CK3000 Sylvania test jig; picture tube 490BLB22 or 19HNP22,used; yoke for a Sears color TV 80-77-4D or Y-268, used. Richard Salazar,10940 Sunnyslope Drive, Riverside, CA 92505.

Needed: Service manual (in English) for NordMende Electronics (German)KM -394 Distortion Analyzer; a working NordMende SRG389 Sine/Squaregenerator; parts/service manual for Sansui SD -7000 R -R tape deck (circa1971); service manual/owner's manuallparts for Acrosound ST -120 poweramp (circa 1958). Steve Bender, Bengrun Research Labs, Box 28360, QueensVillage, NY 11428.

For sale: B&K Model 415 solid state sweep/marker generator and B&Kmodel 1077 TV analyst, both complete with cables, owner's manuals andschematics; both for $150 plus UPS delivery charges. William D. Fowble,217 W. Desoto Drive, Harbour Heights, FL 33950.

Needed: Chroma IC Philco P/N 46-5002-5 or -21 or Sylvania ECG 782 orGEIC-224 or Workman 2057. Will pay going rate and shipping. Bud TV &Stereo, 18480 S.W. TV Highway, Aloha, OR 97006.

Needed: Schematic and parts list for Supreme Instruments Corporationtube and set tester, model 504A. Will purchase copy or original, or willcopy and return. Harold J. Helm, Economy Sales and Service, 40 Monu-ment St., Freehold, NJ 07728.

Needed: Sencore VA -48 TV analyzer, Sencore SG -165 stereo analyzer withoriginal box and manuals. Chuck Vostry, 111 Grenadier. Franklin, TN37064.

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For sale: Commodore Vic 20 computer game cassettes, large selection, lowprices. Send SASE for list. Don Maurer, 2352 Grace Ave., Lebanon, PA17042.

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Linear ICs show analogcan do the job

Some people are under the im-pression that analog circuits aredead and gone, having been com-pletely displaced by digital elec-tronics. Makers of linear ICs canattest that the analog world is notonly alive but thriving. Even manydigital instruments require ananalog subsystem for data acquisi-tion. There are cases where linearIC devices will do a job better orcheaper than a digital circuit,while in still other cases the analoglinear IC is the only way to do thejob. This article will cover linearICs, how they are used and how totroubleshoot those you suspect arebad in a circuit. The ubiquitousoperational amplifier (op -amp) is agood place to start.

by Joseph J. Carr

Op -amp basicsThe operational amplifier was

originally designed to performmathematical operations in analogcomputers. Although analog com-puters aren't used today, the prop-erties that made the op -ampsuitable for that application alsomake it highly useful in a widevariety of do and ac circuits. Somemodern instruments, incidentally,are little more than fixed -programanalog computers.

Figure 1 shows two different cir-cuit symbols commonly used foroperational amplifiers. The ver-sion in Figure la is the one mostcommonly encountered, whileFigure lb is used by a few com-panies and is technically the of-

ficial symbol. The only significantdifference, however, is that onehas a straight back, and the otherhas a curved back. The terminalsare the same on both. The pinoutsshown in Figure la are the so-called industry standard. Theydon't fit all op -amps,sufficiently common to warrantcomment. Originally they wereused on the 741 device but are nowfound on op -amps of all qualitylevels.

The V + and V - terminals arethe power connections. Note thatthere is no ground terminal on theop -amp. The V+ is an independentpower supply that is positive withrespect to ground, while V - isnegative with respect to ground,

INVERTINGINPUT

NON INVERTII,INPU!

A

OUTPUT

INVERTINGINPUT

NON INVERTINGINPUT

Bv_

OUTPUT

Figure 1. Op -amps have one inverting input and one non -inverting input. A is the most commonly usedop -amp symbol; B is used by a few companies.


0.l. F

C24 7,F

- COMMON(GROUND,

C4O.1,F

Figure 2. The power supplyused for an op -amp must bebipolar.

even though no separate groundconnection exists on the op -amp.

The output terminal is self-explanatory. The output signal willswing positive or negative be-tween certain limits less than V -and V+.

The inputs on almost all op -ampsconsist of a pair of differential in-puts. In theory, only the invertinginput is needed, but all commonop -amps also have the noninvert-ing input.

The difference between the twoinputs is a matter of phase. The in-verting input produces an outputsignal that is 180° out of phasewith the input signal. In otherwords, a positive voltage applied tothe inverting input produces anegative output voltage (the in-verting input is marked with aminus sign). The noninverting in-put, which is marked with a plussign, produces an output that is inphase with the input signal. Apositive voltage applied to the non -inverting input will produce apositive output voltage.

Since the op -amp output mayhave to swing either positive ornegative, a bipolar do power sup-ply is needed. Figure 2 shows atypical power supply for an op -ampcircuit. Although batteries areshown here, in most cases elec-tronic power supplies will be used.Note that there are two separate

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November 198'3 Electronic Servicing & Technology 41

power supplies: V + and V - . TheV + supply is positive with respectto common, while V - is negativewith respect to common. Thepower -supply common is also usedas the signal common, and mayalso be the ground (chassis) con-nection.

The capacitors shown in Figure2 are not always used, but areneeded in many cases for power -supply decoupling. The capacitorsare always good practice and areespecially needed in multi -stagecascade circuits, when high fre-quency (uncompensated) op -ampsare used, or where the power sup-ply lines may be noisy.

There are two capacitors on eachline in Figure 2. The high -valuetype is used for low frequencies,while the low -value one is for highfrequencies. The low -valuecapacitor should be mounted asclose to the body of the op -amp aspossible. If multiple op -amps areused, a separate pair of 0.11iFcapacitors is needed for each op -amp.

The one case where thecapacitors are not always used ison frequency -compensated (uncon-ditionally stable) devices such asthe 741. Those types of op -ampstrade off frequency response infavor of stability, so they will onlyoperate properly to 8 or 10kHz.

Ideal op -ampsAn ideal op -amp would exhibit

the following properties: zero noise contribution infinite frequency response infinite open -loop gain zero output impedance infinite input impedance differential inputs "stick

together"The first two ideal properties are

never approached, but are thrownin for benefit of the purists whowould insist, correctly, that suchfactors affect performance.

The third property tells us thatthere is no limit to gain. In real

devices, open -loop voltage gains(AVOL) range from 200,000 to morethan 1,000,000. An implication ofthis condition is that closed -loopgain is controlled totally by thefeedback network.

Zero output impedance (Z = 0)means the output will function asan ideal voltage source. Realdevices usually have Z values ofless than 10012.

If infinite input impedance couldbe achieved, neither input wouldeither sink or source current. Realdevices have Z. value of 1M( to101212, and so will be consideredideal in most cases.

The final condition requiressome explanation. The differentialinputs must be treated mathe-matically as if they were at thesame potential. If a voltage is ap-plied to the noninverting input, forexample, the same potential will befound on the inverting input. Thisis not just some theoretician's con-cept, but can actually be measuredwith a voltmeter. The property isthe most frequently used in oursimplified circuit analysis.

Inverting followersFigure 3 shows the op -amp con-

figuration called the invertingfollower. The noninverting input is

grounded and so is at zero poten-tial. The signal is applied to the in-put resistor, R,.

Because of Kirchoffs CurrentLaw (KCL), we know in Figure 3that I2 = I1 (the ideal op -ampdoes not draw current). We alsoknow from Ohm's law that

L

=and

I2 = Vo/R,

KCL tells us that these equationsare equal:

V,,/R, = - V,,,/R,

The transfer function of a circuitis the ratio of the input voltage tothe input voltage (Voy,/V,,,), and iscalled the gain (A,). Solving forthis ratio yields:

- V,/V, = R,/R,or

- A = R,/R,

These equations tell us that thegain is set only by the ratio of R2 toR1. The minus sign indicates thatphase reversal takes place.

An exampleSuppose we need a gain of -100,

and an input impedance of 10K.

Figure 3. The gain of the op -amp inverting follower circuit is set bythe ratio R2/R,.


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Rearranging the equation for A,will allow us to find R2 that willyield a gain of -100.

R2 = - AR,R2 = -(- 100i ( l OK)R2 = 1000K = 1M9,

In the example above, we usedthe value of R, as the amplifier in-put impedance. This is truebecause point A is essentially atground potential due to thegrounding of the noninverting in-put. Even though point A ofFigure 3 is not actually grounded,it behaves as if it were grounded.This situation is called a virtualground.

A problem with the invertingfollower circuit is that the max-imum input impedance is limited tothe value of R,. In some practicalcircuits, this value can be some-what low. A solution to the prob-lem is the noninverting followercircuit.

Noninverting followersThe noninverting follower cir-

cuits of Figure 4 apply the signalto the noninverting input of theoperational amplifier. There aretwo configurations: the unity gain(4a) and with gain (4b).

The unity -gain noninvertingfollower of Figure 4a has a voltagegain of one because it uses 100%negative feedback. Uses of this cir-cuit include buffering with neitherloss of voltage amplitude norchange of phase, and impedancetransformation made possiblebecause of the high input im-pedance and low output im-pedance.

Because Vo,,, = V;,,, and the out-put impedance is very low, wemust conclude that the unity -gainnoninverting follower does offerpower gain, even though voltagegain is unity.

The circuit in Figure 4b is anoninverting follower with gain.Using an analysis similar to that

used above for the inverting case,but taking into account that pointA is at a potential equal to V;,,rather than ground, we arrive atthe following gain equation:

Av = R2/R, + 1

The gain version of the circuitcan be used for exactly the same

applications as the unity -gain ver-sion, but with voltage gain as wellas power gain.

Op -amp problemsPractical op -amps do not match

the idealized version. One majorproblem is output offset voltages.This term means that the outputvoltage will be nonzero at a time

A

VI

B

R1I,

11 = 11

(Vout - Vin)/R2= VInIR1

Vout -Vin = R2 Vin/R1

R2

Vo

Vout = R2 Vin/R1 + Vin -

Vout = Vin (R2/R1 + 1)

Av = VoutNIn = R2/R1 +1

Vo

Figure 4. The non -inverting follower op -amp circuit may be usedas a buffer or impedance matching device by making the feedbackresistor equal to zero (A). If the circuit is connected as in B, gain wilbe Ay= R2/R, + 1


when it should be zero. For exam-ple, if V, = 0, then V,., should alsobe zero. In many cases, however, itwill not be zero.

There are several causes of out-put offset voltages; among themare the input bias currents. Ifbipolar transistors are used in theinput stage, their bias currents willbe available at the (-) and (+) in-put terminals. In that case, the in-put impedance is not infinite.Figure 5 shows a simple methodfor reducing the effect of this cur-rent. The output offset is causedby current from the (-) input flow-ing in R, and R2, creating an inputoffset voltage that is amplified bythe gain. If we force the bias cur-rent from the (+) input to flow inthe same resistance, it will pro-duce an equal but opposite offsetvoltage, and the two cancel eachother. The net result is zero.Resistor R, in Figure 5 is called acompensation resistor and servesthis purpose. Resistor R, has avalue equal to the parallel com-bination of R, and R2.

The method of Figure 5 solvesonly one form of output offset volt-age problems. Those of Figure 6,however, solve all forms of normaloutput offset voltage problems, in-cluding that caused by input biascurrents.

Figure 6a shows a circuit that isused when the op -amp is equippedwith a pair of offset null terminals(not all so equipped). A poten-tiometer is connected between theoffset nut terminals, and its wiperis connected to the V - power sup-ply terminal. This potentiometer isadjusted to produce V,,,, = 0 whenthe V,0 input is shorted to ground(or common). Alternatively, thepotentiometer is sometimes ad-justed for V,y, = 0 when the (- )and (+) inputs are shortedtogether.

A more universal scheme isshown in Figure 6b. Here we nullthe natural output offset by usingthe potentiometer to introduce acounter -offset of a magnitude andpolarity to completely cancel theoffset voltage. Adjustment of the

R1

'bias

V1 = V2 IfR3 = R1 parallel with R2

Iblas

R3

Al

R2

Vr

Figure 5. If bipolar transistors are used in the input stage of theop -amp, their bias currents will cause an output offset voltage. Ad-dition of R3, equal to the parallel combination of R1 and R, will com-pensate for this offset.

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November '


983 Electronic Servicing & Technology 45

A B

R3

Figure 6. Some op -amps are provided with a set of offset -null terminals to provide for output -offset com-pensation.

A

C

A B

B

V

Cl

R1 R2

- 1

D

Figure 7. Op -amps will oscillate under some conditions. It may be necessary to limit the frequency of theop -amp by adding external components in order to preclude oscillation.


potentiometer is accomplished bysetting the input voltage to zero(shorting the input(s) to ground).The potentiometer is then adjustedfor an output voltage of zero.

Frequency compensationSome operational amplifiers

have such limited frequencyresponse that they are said to beunconditionally stable. A 741device, for example, operates onlyto a few kilohertz. Others, how-ever, have much wider band-widths, and under some circum-stances will oscillate at some

natural frequency. For theseamplifiers, other means must befound. Figure 7 shows severalmethods for reducing the frequen-cy response.

Figure 7a shows the use of acapacitor across a pair of frequen-cy compensation terminals (whichare also sometimes the do offsetterminals. Typical values for thecapacitor are 10pF to 1000pF.Figure 7b shows a feed -forwardcapacitor between a compensationterminal and the output terminal.In Figure 7c we have an RC net-work between the compensation

terminal and ground. The finalmethod, in Figure 7d, shows acapacitor shunting the feedbackresistor. At low frequencies,where X, is much higher than Ref

the gain is essentially R2/R,, or(R2/R, + 1) in noninverting follow-ers. At higher frequencies, thegain falls off at a rate of - 6dB/oc-tave. The frequency at which thegain starts falling off is measuredfrom the - 3dB frequency as de-fined by:

f = 1/27rR2C1

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Test

your electronic

knowledgeBy Sam Wilson, ISCET test director

These questions are similar toquestions used on the various CETtests. All questions on the actualCET test are multiple choice, anda grade of 75% or better is re-quired for passing. This month'squestions are all about power sup-ply. (Answers on page 57)

1. Which of the following is trueregarding the rectifier diodesin Figure 1?A. The diode -resistor combi-

nation doesn't make sense.B. The combination assures

equal forward voltagesacross the resistors.

C. The combination assuresequal reverse voltagesacross the resistors.

D. The PIV of the combina-tion is the same as thelowest PIV rating of thethree diodes.

E. The PIV rating of the com-bination is the same asthe highest PIV rating ofthe three diodes.

4.

2. Which of the following is thepurpose of the resistor in therectifier diode -resistor combi-nation of Figure 2?A. Limit the forward current 5.

through the diodes.B. Assure that both diodes

will conduct.3. Which of the following is true

regarding the rectifier diodesin Figure 2?A. The diode -resistor combi-

nation doesn't make sense.

B. The combination assuresequal forward voltagesacross the resistors.

C. The combination assuresequal reverse voltagesacross the resistors.

D. The PIV of the combina-tion is the same as thelowest PIV rating of thetwo diodes.

E. The PIV rating of the com-bination is the same as thehighest PIV rating of thetwo diodes.

The circuit of Figure 3 isA. a discriminator.B. a ratio detector.C. a full wave rectifier.D. a voltage doubler.E. two half -wave rectifiers.The broken line between theprimary and secondary wind-ings in Figure 3 representsA. a self -resonating

transformer.B. a saturable reactor.C. an auto transformer.D. Faraday shield.E. a phase shifter.


6. The purpose of the 4.79resistor in Figure 4 isA. to limit the output voltage

to a given value.B. to improve the supply

regulation.C. to protect the diode.D. to protect the output load

resistance.E. None of these choices is

correct.7. The output voltage of the

supply in Figure 4 should beaboutA. 140V.B. 100V.

8. In the circuit of Figure 4you will find the audio poweramplifier connected to whichpoint?A. aB. b

9. All of the diodes in the circuitof Figure 5 are silicon types.Which of the following is trueregarding this circuit?A. The output is short cir-

cuited.B. The diodes are connected

in the reverse direction.

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The diode current must beequal to the load current.In order for the circuit towork properly, VIN mustbe at least 25V.The output voltage isabout 2.1V.

10. The circuit in Figure 6 isA. a short circuit across the

secondary.a bridge rectifier.an open circuit.a preregulating circuitand full -wave rectifier.ok if all of the diodesare reversed.

B.C.D.

E.

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Understandingdecibels and

time constantsThe two previous articles in this

series (August and OctoberES&T) have covered the inventionof logarithms and their relation-ship with epsilon (e). In this article,we will show how epsilon is relatedto the charge of a capacitor.

Why study math?Mathematics is a shorthand

method of expressing relationshipsin electrical and electronic circuits.Technicians should think ofmathematics as being an aid(rather than a hindrance) toanalyzing electronic circuits andsystems. Unfortunately there is somuch new technology to belearned that the importance ofbasic mathematics relationships isoften underestimated.

I have heard technicians boastthat they have worked many yearsin electronics and never even usedOhm's Law.

Suppose a technician measuresthe voltage across a resistor andfinds that voltage is too low ac-cording to the manufacturer'sspecifications. He immediatelyknows that the current orresistance (or both) is too low. Heknows that because he knowsOhm's Law. He knows that thevoltage across a resistor dependsdirectly upon the current andresistance. In other words, heknows that V = I x R.

Every time a student learns anequation, he is learning a short-hand method of remembering rela-tionships in circuits. Imagine try -

By Sam Wilson, ISCET test director

SW

V

Figure 1.

ing to learn about electronics bydealing with Ohm's Law stated,"The amount of voltage dropacross a resistor is dependent uponthe amount of current flowingthrough that resistor, and it is alsodirectly dependent upon theamount of resistance of thatresistor."

Can you imagine having to learn20 or 30 laws similar to that beforeyou could begin to understandbasic electric circuits? Fortunatelyyou don't have to. The simple equa-tion V = IR tells it all.

Time constantsHow was the time constant

equation (T = RC) obtained? Con-sider the circuit of Figure 1. Thecapacitor is discharged. It willstart to charge the instant theswitch is closed. The mathematicalequation for the voltage across thecapacitor (ve) at any instant of timeafter the switch is closed (t) is:

ye= (1- 1 ) VetrRC

Where V is the applied voltage, Rand C are the resistance andcapacitance in ohms and faradsrespectively, and e is epsilon(2.71828).


A special case occurs when t is capacitor is discharged to start.)made equal to R x C.

t = RC= 1RC RC

For t = RC, the equation becomes:

vc+ (1- 1 )VedRC

_ (1- 1 )Ve'

_ (1- 1 )V2.71828

v,= 0.632V, or, v,=63.2% V

This equation shows that thevoltage across the capacitor is63.2% of the applied voltage whent = RC. That is the reason that thevoltage on the capacitor after onetime constant equals 63.2% of the,applied voltage.

An important thing to note fromthis discussion is that e is a factorin calculating the growth ofvoltage across p chargingcapacitor. This peculiar number(2.71828) is related to many fieldsother than electronics and biology.

The time constant equation (T,=R x C) is useful when you want tofind how long it takes a capacitorto charge to 63.2% of the appliedvoltage. But how do you find thevoltage across the capacitor forsome other value of time? If youhave a calculator, it is a simplematter to use the equation for v,. Ifyou do not have a calculator,follow the step-by-step procedureto increase your insight into thetime constant.

Sample problemIn the circuit of Figure 1, the

following values apply: V= 5V,R= 1Mt1 and C =1µf.

What is the value of v, 0.5s afterthe switch is closed? (For this typeof problem, always assume the

SolutionThe time (t) is 0.5s, and the value

ofRxCis:

RxC = 1x10°x1x10-°

orRxC = is

The equation can now be solved:

v,= (1- 1)V

e ./RC

= (1- 1 )x5eo.aii

V = 1.97V

So, in 0.5s the voltage across thecapacitor has increased to slightlyless than 2V.

The equation for v, can be usedfor many practical problems.However, in technicians' books,T, = R x C is often given as the on-ly time constant equation. And forfull charge of the capacitor, theequation is given as T, = 5 x R x C.

Is the capacitor really charged tothe full supply voltage in five timeconstants? Not quite. If you use t= 5 in the equation for v,, you willfind that the voltage across thecapacitor is 99.3% of the supplyvoltage at the end of five time con-stants.

So when does the capacitor ac-tually become fully charged?Never. You can raise e to any largenumber and if your calculator canwork with that number, you willfind that the capacitor is not quitecharged to the full supply voltage.

The value of five time constantsfor full charge was chosenbecause, for all practical con-siderations, the capacitor is fullycharged after that amount of time.

Arriving at the equationsHow did they arrive at the equa-

tion for decibels, time constantsand Ohm's Law? The curve for theresponse of the human ear toloudness and the curve that shows

the voltage across a capacitor dur-ing charge are both logarithmic.

If you were an early ex-perimenter working on hearingmeasurement and graphed yourresults, you would soon come tothe conclusion that the generalshape of the curve is the same forall people with normal hearing. Ifyou had a basic math background,you would recognize that you aredealing with a logarithmicresponse, so you would write anequation that involved logs for thehearing response.

The process of writing an equa-tion from a curve is called curve fit-ting. This is not to play down thevaluable contribution of the peoplewho did this important work. But,technicians are sometimes puzzledabout where certain equationscome from.

You could not derive the equa-tion for decibels without first mak-ing a lot of measurements to seewhat type of response you aredealing with. Equations that arederived this way from data arecalled empirical equations.

The equation for V, was derivedthe same way. Data was taken andcurves were drawn, then the equa-tion that fit that curve was writ-ten. Therefore, V, is an empiricalequation.

It is interesting to note thatOhm's Law (V = IR) was derivedempirically. Georg Ohm lived inthe shadow of his brother, whowas a famous biologist in Europe.

Ohm studied the relationshipbetween voltage and current, thenwrote an equation that related thetwo. His first published paper gavean equation that was not correct.Fortunately, he reworked theequation and soon published it inthe form we use today.

So far in this series we havetalked about the concept ofdecibels and time constants. In afuture issue, we will continue withthe time constant equations andthen give examples of practicalproblems that can be solved withthe equations discussedup to this point.


Troubleshootingsymmetrical

output circuitsThe most common type of audio -

output circuit uses two transistorsin what is commonly called a push-pull or complementary arrange-ment. There are many specific ex-amples of circuits of this type, butfortunately only three basic varia-tions on the theme. These are thepush-pull transformer -coupledtype, the true output -transformer -less (OTL) type and the most com-mon of the three, the quasi -complementary type.

The easiest to understand is thegarden-variety transformer -drivenoutput stage (Figure 1). You willcome across this circuit or its closecousins in all tube circuits, oldertransistorized products and less -expensive products. Because a ma-jority of the products in the servicemarket now are solid state, we'lljust look at transistor circuits, butthe exact same analysis applies totube circuits.

The output transformer is drivenby both Ql and Q2. The signal in-verter make the top and bottomsignals fed to each device a mirrorimage of each other because theyare 180° out of phase. Each deviceis biased into cut-off either half ofthe time (pure class B operation)or slightly less than half of thetime (class AB operation). Thisoverlap in conduction is created inorder to eliminate crossover distor-tion, which can occur if one deviceturns on as the other turns off.This can be easily observed on thescope as a "notch" appearing as thewaveform crosses the zero -conduc-tion point.

When either transistor con-ducts, it induces a voltage acrossthe entire transformer primary,which is then coupled to the trans -

By Bud Izen, CET/CSM

former secondary and thereforeappears across the speaker. De-pending on the design choice madeby the manufacturer, the out -of -phase signals used to drive eachdevice may be furnished by asingle inverter stage, which af-fects only one of the output devices(the bias makes sure when eachone starts to conduct), or may befed by an input transformer. Sucha transformer provides twosignals, each 180° out of phasewith the other (Figure 2).

Transformer couplingThe disadvantages of using

transformers are phase distortiondue to the reactance of the trans-former, loss of low -frequencyresponse due to core loss, weightincrease, increased cost and theresulting increase in product size,and energy consumption due totransformer inefficiency. Themain advantage of using trans-formers is ease of design, and alesser advantage is that short cir-cuits in the driver stage areisolated from the output stage andvice versa. For this reason,troubleshooting is fairly straight-forward.

A more complex circuitNeither of the circuits of Figures

1 or 2 are practical enough towork, yet they are not far from be-ing usable. A realistic circuit usinga single transistor as a phase split -ter is shown in Figure 3. Thesignal at the collector of Q1 is 180°out of phase with that on the base,which can be treated as being incommon emitter configuration.The signal at the emitter is inphase with that at the base, and

can be thought about as being incommon -collector, or emitter -follower configuration.

The gain of the Q1 stage is set bythe ratio of R3 divided by R4, andis adjusted so that the signals fromcollector to ground and emitter toground are essentially equal, andopposite in polarity. Ql and Q2 arethen biased into class B or ABoperation by resistors R5 and R6.Capacitors Cl, C2 and C3 arenecessary in order to avoid quies-cent operating point shift. Al-though more parts are required toaccomplish this design than theprevious one, frequency responseis better and the cost is lower.

The complementaryoutput circuit

Figure 4 shows a somewhatmore complicated design that re-quires neither a phase -splitting de-vice nor a transformer. By usingone NPN and one PNP device(each the other's complement),push-pull action occurs withoutany external help. The two tran-sistors are placed in series acrossthe do power supply. Resistors R3and R4 provide fuse protection andsome amount of thermal stability.R1 and R2 provide base currentpaths at the proper time.

Diodes Dl and D2 (often part ofa single unit) provide bias stabilityin the following manner. Undernormal conditions, the two tran-sistor bases are about 1.2V apart.In an NPN device, the base is nor-mally 0.6V more positive than theemitter, while in a PNP device thebase is 0.6V more negative thanthe emitter. Ignoring the smalldrop across R3 and R4, the basesshould measure normally about


SIGNALINVERTER

Zvcc

Figure 1. A push-pull output driven by a signal inverting stage.

O, output

0, output

Figure 2. A push-pull output driven by a phase -splitting driver transformer.

VCC

Cl

Figure 3. A circuit using a single transistor as a phase splitter.

Figure 4. A basic complementary -symmetry amplifier with ther-mal stabilization.

1.2V apart constantly because theemitters are essentially tiedtogether.

The diodes are mounted verynear the output transistors, oftensecured to them or mounted on thesame heat sink. The temperatureresponse of the diodes is matchedto that of the transistors. As thetemperature of the devices in-creases, causing the transistors toincrease in conduction, the voltageacross the diodes decreases,limiting base current. Therefore,thermal runaway can be con-trolled.

Avoiding a critical errorA word of caution is necessary at

this point. Because the diodes arematched to the output devices, if itis ever necessary to replace thediodes, use only exact replace-ments. Also, if new output devicesare required in circuits like this, itis wise to order the diode unit(s) aswell. In the case of a part numberor type change when the orderedparts are received, this will ensurethat a repair brings the unit backto specs without worry or un-necessary delay. There is nothingmore annoying than to installsubstitute devices with differentnumbers than the original partsand have the unit fail because thetemperature characteristics of thediode are not the same as that ofthe replacement device.

Obviously, the same caution ap-plies when using general sub-stitutes for original parts. Theymay or may not work, even if the


Figure 5. The circuit of Figure 4 preced-ed by a class -A voltage amplifier.

manual says they will. In general,you will always be better off re-placing output devices with exactreplacements. The higher thepower of the amplifier, the morelikely this is to be true. If theamplifier is direct -coupled, thiswill be crucial in avoiding disaster.

To illustrate this, the servicemanager of a local branch of achain stereo store told me that oneday a local servicer came in to dropoff an amplifier. The servicer com-plained that the "darn thing justwasn't any good," and was "im-possible to fix." He had replacedvirtually every transistor in theunit with a well-known generalsubstitute device.

Unfortunately, the amplifier wascompletely direct coupled. All ittook was a little bias shift, andevery single substitute device wasdestroyed. Replacement of thetransistors with exact replace-ments and output current adjust-ment was all it took to repair theunit.

The analysis continuesBecause the output of the circuit

in Figure 4 is taken from the emit-ters, no matching transformer isneeded. However, because the de-sign requires that half of the dosupply voltage be dropped acrosseach device, steps must be taken tokeep de out of the speaker. C2 is

vec added to block do from pass-ing through the voice coil, whichotherwise would cause core satura-tion and possible coil burnout.

If you work on a speaker thathas been burned out, don't forgetto suggest to the customer that the

amplifier should bechecked for possibledc presence. Like-wise, it is alwaysnecessary to checkfor presence of ex-cessive de on speaker

lines each time an output circuit isrepaired. Usually a maximum dolevel is given on the schematic orin the adjustment procedures. Iwould suggest that no more than0.025V be present.

Becoming more practicalThe circuit of Figure 4 is still not

quite practical, but is close.Because Ql and Q2 are emitter -followers, the output stage has avoltage gain of slightly less thanone. It is therefore necessary toprovide at least one stage ofvoltage gain before the output.Figure 5 shows the circuit ofFigure 4 redesigned with Q3 addedas a pure class -A voltage amplifier.R3 and Rl couple back negativefeedback to stabilize the gain of Q3by monitoring a rise in voltage at

Rq

.R5

the junction of C3, R6, R7 and R3.The Q3 operating bias is obtainedthrough that same source, whileobtaining collector bias from R5,D2 and Dl. C2 is provided toeliminate any signal voltage feed-back. This circuit is now practicalenough to find application in manysorts of products, but it can berefined further.

Disadvantages ofcoupling capacitors

Coupling capacitors have severalundesirable characteristics. Theycause phase distortion becausethey have more reactance at lowfrequencies than at high frequen-cies. Coupling capacitors that areused to couple the signal from out-put devices to speakers whileblocking de must be very large insize (often thousands of micro -farads) because of the low im-pedance nature of output circuits.In order to avoid pronouncedphase shift and accompanyingvoltage -divider action, thecapacitive reactance should be nomore than 10% of the speaker loadresistance at the lowest operatingfrequency. If such is not the case,loss of bass response is often theresult. Physically large capacitorsare expensive and limit the overallcompactness of the amplifier.

R3

Figure 6. dc -coupled complementary amplifier.

±


Figure 7. Quasi -complimentary sym-metry.

A solution to the problemsFigure 6 shows the circuit of

Figure 5 modified to eliminate theneed for all coupling capacitors.Instead of using one source of Vcc,the original Vcc is divided into twosupplies, one negative and onepositive. Initial engineering of theoutput transistor biasing will en-sure that the speaker output linewill have essentially 0Vdc onit. Transistors Q4 and Q5 are add-ed as a differential pair. As long asthe speaker line remains at 0Vdc,Q5 essentially does nothing. If thevoltage on the speaker line rises(in either the positive or negativedirection), Q5 will change conduc-tion so as to restore balance. R4serves as a constant currentsource for Q4 and Q5, allowing thisaction to occur.

The voltage on the speaker lineis referred to as the offset voltage.The offset voltage is monitored bythe current flowing through R5.The do levels can then be altered,depending upon the direction ofoffset shift.

Troubleshooting analysisAs an example, let's examine

what would happen if the offsetvoltage increased negatively. Q5would turn on harder, its collectorvoltage would fall, increasing the

drop across R3. The voltage at thebase of Q3 would be less negative,turning on Q3 more and loweringits collector voltage. In turn Qlwould turn on harder and Q2would conduct less, regaining zerooffset. In order to analyze thereverse situation, a positive in-crease in offset voltage, merelychange the words in the aboveanalysis. Change up to down, fall

to rise, less to more, harderto less hard and low-ering to raising. The

final result is the same:restoration of zero offset.

Improving damping factorThe application of a concept

called damping factor is a majorconcern to users and manufac-turers alike. In order for theamplifier to be able to controlspeaker cone movement, the ratioof speaker impedance to amplifieroutput resistance must be fairlyhigh. Elimination of the outputcapacitor improves that ratio asthe capacitive reactance increasesthié output impedance when such acapacitor is used. Because the cir-cuit of Figure 6 accomplishes thistask, you will find its application inmany high -quality amplifiers. Cir-cuits such as these produce damp-ing factors from 20 to 50 andabove.

More power neededUnfortunately, with few excep-

tions, complementary NPN-PNPpairs are hard to match for high -power applications. Above 10W orso, NPN power types become ex-pensive, too. Factors liketemperature coefficient and betadrift become critical in high -powerapplications, and slight discrepan-cies in such characteristics usuallyresult in catastrophic failure.When high power is needed, acomplementary pair is often usedas a driving stage, while two NPNtypes are used to actually providethe power. This type of circuitry iscommonly called quasi -complemen-tary symmetry. Circuits combin-ing the features of both circuits inFigures 6 and 7 are common.

Figure 7 shows a typical, simpli-fied but accurate representation ofsuch an output configuration.When a positive voltage is present-

ed to the base of Q1, increased con-duction takes place in both Ql andQ3. Notice how the collectors of Qland Q3 are tied together and thatthe emitter of Ql feeds the base ofQ3. This is called a Darlington -pairconfiguration. Sometimes manu-facturers provide such a pair in asingle conventional 3 -leadpackage. Watch out for this inmaking substitutions. The netresult is that Ql and Q3 acttogether to simulate a high -powerNPN device.

Similarly Q2 and Q4 are connect-ed to simulate a high -power PNPdevice. When a negative signal ispresented at the base of Q2, itturns on, making the voltage on itscollector less positive and causingQ4 to conduct harder.

In order to stabilize the voltagedrop between the bases of Q1 andQ2, diodes Dl through D3 areused, often integrated into a singlepackage as previously discussed.Three diodes are needed becausethere are now three junctions tostabilize (Q1, Q2 and Q3).Resistors R1 through R5 are usedto provide thermal stability andfuse protection. They are notalways used in such circuits. In allrespects, these types of circuitscan be analyzed just the same wayas the true complementary circuitspreviously discussed.

A final cautionAfter the repair of an output cir-

cuit of an audio amplifier, it isvitally important to make sure thatthe cause of failure is not external.Many times output circuits can beblown by shorted speaker wires,an excessive number of speakersbeing driven by the unit, or bysomething defective in one of thespeakers themselves. Many ser-vicers I know will not warranty anoutput circuit repair unless thecustomer brings in the speakerwire and sometimes even thespeakers themselves. Doing any-thing less is taking a gamble.

It is also entirely possible thatwhen the output stage failed, thespeaker system was simultaneous-ly damaged. Failure to check outthis possibility leaves you opento all kinds of unpleas-ant possibilities.


IMIII-~...-.r

Symptoms and cures compiled from field reportsof recurring troubles

Chassis - RCA CTC108PHOTOFACT - 2030-2

U701

LUM CHROMA

+11V

2200 4

TP806

Q702

VERT BLANKER

R710

3900 it

OPEN

R709 R712 A/PULSES

56K (47KI

Symptom -Normal sound, but no rasterCure -Check resistor R712, and replace it if open orincreased in value

1 i Chassis RCA CTC53Ei PHOTOFACT-1201-1 or 1342-2

Chassis - RCA CTC76PHOTOFACT -1468-2 or 1616-1

CR4 CR2

3

FROM T101 +82 5V

CR5 CR3

C103C i_750µFR

\ OPEN

Symptom - Insufficient height at bottom and erraticvertical rollingCure -Check filter capacitor C103C, and replace can ifany section is open

Chassis - RCA CTC111 5PHOTOFACT - 2038-1

+11 4V

Q3

RED

R12

1000 4

L3

27K

R6

R3

22009

12K

2W

+ 211V

CRT RED

CATHODE

PIN 8

SGI 5

SHORTED

Symptom - Bright red screen with retrace; shut -downafter a few secondsCure -Check spark -gap SG1-5 on the kine-drive board,and replace it if shorted

r

r

C6

022µF

C7

0.01µF

R16

1800 it

R18 220K

C12

82pF 120K

R33 1000 4

Q3 R19 180KSYNC SEP

R17 680K

+ 17.5V

Symptom - Erratic horizontal pulling in pictureCure - As a test, replace Q3 sync separator

+ 265V

REPLACE

R45

2

Chassis - RCA CTC97PHOTOFACT-1862-1 or 1931-2

Q15

COLLECTOR

SIR114 1M 12

SERVICE o

BAD CONTACTS -32 2V

Q16

VERT OSC

R103

4

Symptom - Intermittent rolling or loss of heightCure -Check the service/normal switch, and replace it ifcontacts are erratic or leaking to ground

Chassis - RCA CTC109 6PHOTOFACT-1952-1

120 VAC

CR101 CR103

CR104

C105 LI00µF

OPEN

+ 162V

SOURCE

Symptom - Receiver began operating by itself andcannot be switched off, also the picture has an hour-glass shape with ac -hum instabilityCure -Check C105 filter capacitor, and replace it ifopen

ti


J

i

Answers to quiz(from page 48)

1. C There is no assurancethat the reverse resis-tances of diodes are equaleven though they havethe same type number. Itis possible that a reversevoltage can be excessiveacross one of the diodesif its reverse resistanceis high compared to theother two. The high -resistance resistors inFigure 1 have identicalvalues and they equalizethe reverse voltage drop.

2. B If one diode has a for-ward voltage of 0.7V andthe other has a forwardvoltage of 0.8V, they can-not be connected directlyin parallel. The reason isthat if the 0.7V diodestarts to conduct, theother one will never haveenough voltage across itto start it into conduc-tion. The resistors assurethat when one diodestarts to conduct, thevoltage across thatbranch will be highenough to start the otherdiode.

3. D4. E Discriminator and ratio

detectors require tunedtransformers.

5. D The purpose of this shield

is to prevent electrostaticcoupling between theprimary and secondary.

6. C In a few cases thisresistor has been used fortwo purposes. It protectsthe diode from the surgecurrent that occurs whenthe capacitors are firstcharged. At the sametime it may be used as afuse to protect the supplyfrom a constant over-load.

7. A The output capacitorcharges to the peakvoltage of the inputminus the drops acrossthe filter, diode andsurge limiter.

8. A Power amplifiers do notrequire a highly filtereddo voltage. By connect-ing the power amplifierto point a, it is notnecessary to have a highcurrent flowing throughthe filter resistor.

9. E With about 0.7V acrosseach diode, the outputvoltage will be about2.1V.

10. A The only limit to thesecondary current oneach half cycle is the for-ward voltage dropsacross the diodes.

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The 12V, 2.5Ah, sealed batteriescome in three configurations:0810-0177 for Sony BP20, 0810-0178 for JVC PBP-1, and 0810-0179 for Sony BP60 systems.Other configurations are availablefor other portable videotapesystems from LCOMP.


Electronic grade coolantAn electronic circuit/component

coolant to aid in servicing videogames and vending machines hasbeen introduced by Chemtronics.The coolant, named Freez-It, isdesigned to make thermal inter-mittent troubleshooting of circuitboards and electronic componentseasier. Applied as an aerosolspray, Freez-It will freeze to-65°F. Rapid chilling of suspectedcomponents allows individual com-ponents to be isolated for instru-ment testing.


Freez-It coolant also can be usedto prevent transformer burnout.Other uses include low -tempera-ture testing of circuits and equip-ment, preventing cold solderjoints, soldering delicate, heat -sensitive components and aiding inshrink -fit assembly


Microcircuit soldering kitA kit including soldering iron,

tips and holder, from Ungar, isdesigned for precision microelec-tronic soldering.

The 9375 Micro -Soldering Kit in-cludes a 3 -wire handle that is slim-mer than earlier models tofacilitate close -tolerance solder-ing, a ThermoDuric heating ele-ment, tips of three different con-figurations and a holder assembly.

9.375 MICROSOLDERING KIT

Thermo-Duric heating elementsreach temperature and recoverquickly, and eliminate electricleakage, which could ruin microcir-cuits. The three precision tips sup-plied in the kit are a needle point(0.005in. diameter at the point), a0.03in-wide spade point and a0.06in-wide screwdriver. Nineother tips are available.


Aerosol flux removerDeveloped for electronic produc-

tion, re -work and repair, Chem-tronics' new aerosol flux remover

speeds the removal of activatedand non -activated rosin flux andionic soils from electronic sub-assemblies, printed circuit boards,switches, connectors and semicon-ductors, silicone wafers and otherelectronic components.

Flux -Off, a highly concentratedCO2 propelled solvent, removestough deposits without harm todelicate components. It will alsoeffectively remove other contami-nants such as dirt, grease andmolding compounds without leav-ing a white residue.


Floppy disc drive maintenanceDumont Magnetic Technology

has announced third -partymaintenance, repair and refurbish-ment service on floppy disc drives.Nearly every variety of floppy discdrive from companies such asShugart, Tandon, MPI and Qumecan be repaired and refurbished tothe companies specifications. Inaddition to complete drive service,Dumont has a head repair facilityand can repair most heads withoutadditional cost.


Capacitance meterThe 3002 autoranging capaci-

tance meter, from GlobalSpecialties, combines the preci-sion, range and flexibility of bench -top models with the convenienceand operating efficiency of ahand-held, portable unit. Thismeter provides direct readings ofcapacitance from 1pF to 19,990µFwith eight automatically selectedranges providing accurate mea-surements of capacitance withoutmanual switching.

The dual -threshold measure-ment technique eliminates readingerrors due to dielectric absorption.By using do charging characteris-

It's no puzzle J \to order Oelrich \7Service FormsFor TV -radio and two-way radio service-legal forms ter Calif., Florida and Utah.

Now at parts jobbers or write for cat B64.

OELRICH PUBLICATIONS4040 N. Nashville Ave., Chicago, IL 60634Now call toll -free! 800-621-0105

PREVENTHI -TECHHEADACHES

Our Isolatorseliminateequipmentinteraction,clean up interference,curb damaging power line spikes andlightning bursts.

ISO -1 Isolator3 isolated sockets; quality spikesuppression; basic protection... $76.95

ISO -3 Super -Isolator3 dual isolated sockets; suppressor_commercial protection 115.95

ISO -17 Magnum Isolator4 quad isolated sockets; suppressorlaboratory grade protection 200.95

Electronic Specialists, Inc.171 S. Main St., Box 389, Natick. MA )1760

Toll Free Order Desk 1-800-225-4876MasterCard. VISA. American Expr3ss


UNIVERSALCRT

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Works with All color CRT testers Checks virtually Every color CRT

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Set-up manual included

Dandy Manufacturing Co.1313 N Main St,

Muskogee, OK 74401918 682-4286

Call Toll Free1-800-331-9658

Circle (24) on Reply Card Circle (27) on Reply Card


Marketplace

1983 I.C. MASTER2 -VOLUME EDITION

The only publication with the answersto your questions on integrated circuitand microcomputer board selection

55,000 entries in the world's mostcomprehensive function -for -function,pin -for -pin I.C. replacement guide.

3500 pages organized by function, type,and key parameters to make finding thedevice which best satisfies a need fastand easy.

For a FREE 6 page brochure about theI.C. Master, call, write or circle reply card.

Active ElectronicsP.O. Box 8000Westboro, Mass. 01581

Toll Free: 1-800-343.0874Mass. Call: (617) 366-0500

Circle (28) on Reply CardATTENTION

ELECTRONIC TECHNICIANS_ Highly Effective Home Study BSEE Degree Pro-

." gram for Experienced Electronic TechniciansOur New Advanced Placement Program grants

:1Fi; Credit for previous Schooling & Professional Ex-' perience. Advance Rapidly! Our 36th Year!

FREE DESCRIPTIVE LITERATURE!

Cook's Institute of Electronics EngineeringDESK 15 , P.O. BOX 20345. JACKSON, MS 39209


aJENSEN TOOLS INC.

Jó155 46Th STREET PhOENIX AZ 85040

FREE CATALOGWARD -TO -FIND PRECISION TOOLS

Lists more than 2000 items: pliers, tweezers,wire strippers, vacuum systems, relay tools, op.tics) equipment, tool kits and cases. Send foryour free copy today!


FREE KIT CatalogTest Equipment -Kit or AssembledFUNCTION GENERATOR Kit $59.95Auto -Ranging Cap -meter kit $79.95

Phone 209-772-2076Circle n1/no, or phone for oattine.

containsTEST &

EXPERI-MENTERS

EQUIP.

RAGE BOXC INSTRUMENTS

144IVALLEY SPRINGS CA 95252Circle (31) on Reply Card

SATELLITE TV VIEWERSGet the most complete weekly listings

Send SI for sample copy.

P 0 Box. 3t-13. Fortuna, Cahlornia 95540800-358-9997 (U.S.) 800-556-8787 (Calif.)

707-725-4476 (all others)

tics to determine true capacitance,the 3002 can determine capaci-tance in cable, switches and otherelectronic components and hard-ware in addition to capacitors andcapacitor networks.


Digital storage oscilloscopeHitachi's VC -6015 digital

storage scope features a memorycapacity of 1000 words per channelwith a writing speed of 1µs perword to lms per word. TheVC -6015 has a pretrigger functionthat enables the capture of anevent before the trigger pulse oc-

curs, a feat that up to now was im-possible with conventional CRT -storage type scopes. The pretrig-ger position may be set at 0, 2, 5 or8 divisions, and the trigger point isdisplayed on the CRT as an inten-sified point, allowing the user todetermine its relationship to thecaptured waveform.


Signal generatorsLeader Instruments has in-

troduced three new programmablesynthesized AM/FM RF signalgenerators. The new series ofgenerators features convenientkeyboard control of frequency andoutput level. Semi -automatic

. ( ..

9 :-zm sti

9999s_ ,<<

© 1

operation is available by pre-pro-gramming up to 100 different testconditions.

The LSG-217 offers an outputfrequency range of 0 to 70MHz intwo bands, 0.1 to 19.9999MHz in100Hz steps and 20 to 70MHz in1kHz steps. Output level range is 0to 120dBµV in 1dB steps.


Portable lightHeadlights, from Brighteyes of

California, are a self-contained,portable light source for the re-pairman or inspector. They directbright light where you look whileleaving both hands free for tools,writing or adjusting. They light

when you put them on, and thereare no switches, cords or batterypacks to snag or break. Headlightsare designed to be worn comfort-ably with or without glasses, andallow you to get as close to thework as you wish.


Digital multimeterA new, 31/2 -digit auto -manual

ranging hand-held digital multi -meter with 0.7% do accuracy,overload and transient protection,high energy fuse, diode test andaudible continuity check isavailable from the B&K-PrecisionTest Instrument Product Group ofDynascan Corporation.

Model 2806 features auto -rang-ing or step -through manual rang-ing for all voltage and ohmmeasurements, and manual rang-ing on amp measurements. The dovoltage ranges are 200mV,2000mV, 20V, 200V and 1000V,and the ac voltage ranges are2000mV, 20V, 200V and 750V.



A. W. Sperry Instruments hasreleased a new full -line catalog,MC -499 Issue A. The catalogfeatures the entire AWS line oftest equipment including

stro,.. V.,0000.1.

,,nPn e.nKa19

oscilloscopes, analog and digitalsnap-arounds, analog and digitalmultimeters, power meters, in-sulation testers, indicating devicesand accessory items.


Etco Electronics has released anew 112 -page catalog featuringthousands of items from the fieldsof electronics, communications,telephone, cable TV and video, inaddition to a complete parts selec-tion for the hobbyist or repairshop.

A 16 -page section of the cataloghas been devoted to telephone andrelated equipment for smallsystems applications as well as forthe home user. Simple systemsthat can be user -installed areshown.


The new 96 -page Fall/WinterCatalog is now available fromMisco. The catalog offers more

than 200 new items and containsthree new product section catego-ries. All products are available forimmediate shipment by phone orupon written order. The companyoffers supplies and accessories forcomputer and word processors, in -

Computer Supplies and Accessories

.,,.41t

hi II

Easy DirecrOrder,ng!TOLL FREE! 1-300.631-2227

eluding a complete line of CleanRoom cleaning and decontamina-tion products.

Circle (101) an Reply Card

FORDHAM DISCOUNTS DISCOUNTPRICES ON HITACHI SCOPES

35 MHz DUAL TRACE

Vertical sensitivity 5m V/div to 5V/divand 1m V/div to 1 V/div with 5Xamplifier Trigger modes Auto-matic, Normal, TV (+), TV(-).

REG $895OUR PRICE

°59WITH PROBES

95

SIGNAL DELAY LINE

_,`, jModel V -352F

TOLL FREE (800) 645-9518

FORD260 Motor Parkway, Hauppauge. N Y 11788

60 MHz DUAL TRACEDELAYED SWEEP

High sensitivity 1 mV/div(10 MHz) 5 ns/div sweep rate 3rd channel display (triggerview) Variable trigger hold -off Full TV trig-gering Singlesweep Auto-matic focuscorrection.

OUR PRICE

$995 Model 650F

WITH PROBES

100 MHz QUAD TRACEDELAYED SWEEP

Large bright 8x10 cm screen Quad trace operation/Ch1. Ch2,A trigger and B trigger Highsensitivity 500 µ V/div (5 MHz) Full TVtriggering

in N.Y. State 800-832-1446 VISA COD Master Charge Money Order N.Y. State residents add Check appropriate sales tax.COD's extra (required 25% deposit)

OUR PRICE Model V -1050-F

51590 -4"--.1~6-WITH PROBES

ADD FOR SHIPPING AND INSURANCE$250.00 .... $4.50

$251.00 to 500.00 6 50501.00 to 750.00 .... 8.50751.00 to 1000.00 ....12.50

over 1000.00 15.00



Opportunity knocks.The professional world of the Electronics Service Dealer is rough.

That's why we're working so hard to make it easier for you to operatea cost effective business. NESDA offers substantial savings on bank -card and insurance rates, business contacts, technical and managementcertification, and that's just the beginning.

Our members are kept informed about industry developments, andare offered the most comprehensive managerial and technical trainingprograms available. Opportunity knocks. Don't let it pass you by.

For more information about the National Electronics Service DealersAssociation, write to: NESDA, 2708 W. Berry St., Ft. Worth, TX 76109.

NAME

FIRM NAME

FIRM ADDRESS

CITY STATE ZIP

Member of State Local Assn.

PHONE

Classified

Advertising rates in the Classified Section are 50cents per word, each insertion, and must be accom-panied by payment to Insure publication.

Each initial or abbreviation counts a full word.

Minimum classified charge $10.00.

For ads on which replies are sent to us for forwarding(blind ads), there is an additional charge of $3.00 perinsertion to cover department number, processing ofreplies, and mailing costs.

Classified columns are not open to advertising of anyproducts regularly produced by manufacturers unlessused and no longer owned by the manufacturer ordistributor.

FOR SALESCRAMBLED TELEVISION, encodingldecoding. Newbook. Theory/circuits, $9.95 plus $1 shipping. Work-shop, Box 393ES, Dept. E, Bethpage, NY 11714.7-80-tfn

TUBES FOR TV AND RADIO -354 ea. Washington TVService, 1330 E. Florence Ave., Los Angeles, CA 90001.

1-83-12t

CABLE TV CONVERTER/DECODER. LOWEST PRICEANYWHERE. Oak N-12 or Jerrold SB-3 replacement$79.00, Combo with 35 channel converter $139.00, Jer-rold DRX-3DIC with remote $179.00. Send $2.00 withorder or for catalog, refundable with your order to: CKElectronics, 397 Route 18 East, Suite 377, EastBrunswick, NJ 08816, 201-739-2671. 10-83-2t

COMPLETE JERROLD WIRELESS REMOTE/DE-SCRAMBLER-full warranty, $159.00. Complete Oakdescramblers, full warranty, $169. Trap/filters in linetype, $49, 2 min. installation, SG613 transistors, only$6.99. Original Toshiba 2SC1172B, only $1.99 withhardware. 100/450, 80/480, 200/300, 40/450, 25 1st only$1 each mixed or single lot. Super special while theylast 800-860 41 each safety caps Zenith type, 10 lot on-ly $2.50. Bulk 2SC1172B only 50 lot, $1.69. RedcoatElectronics, 104 -20 -68th Drive, Forest Hills, NY11374, (212) 459-5088. 5-83-tfn

CABLE CONVERTERS, DECODERS. Free catalog!APS, POB 263, Newport, RI 02840. 6-83-12t

SUBSCRIPTION TV MANUAL, covers all three majorscrambling systems, only $12.95. Includes theory, cir-cuits,. waveforms and trouble shooting hints. Saveyour VIDEO GAME CARTRIDGES on EPROM with ourEPROM duplicator. Plans $9.95. Catalogue $2.00,refundable. RANDOM ACCESS, Box 41770A, Phoenix,AZ 85080. 8-83-tf n

2SC1172B's, 50 LOTS-$1.699; 2SC1308K's, originalSanyos, 50 lots-$1.99; Cheater cords, 25 lots -354;poi- and non -polarized. 1,000 ft. reels of RG 59 U. CoaxCable-$39/roll. Minimum order $75. Redcoat Elec-tronics, 104-20 68th Drive, Forest Hills, NY 11375,212-459-5088. 10-82-tfn

ELECTRONIC SURPLUS: CLOSEOUTS, LIQUIDA-TIONS, Parts, equipment stereo, industrial educa-tional. Amazing values! Fascinating items unavailablein stores or catalogs anywhere. Unusual FREE catalogETCO.011, Box 762, Plattsburgh, NY 12901. 6-78-tfn

SPRING SPECIALS on Popular Electrolytics-40/450V-754; 80/450V-854; 100/450V-954 200/300V-$1.05. Quantity 20 lot only. Minimum order of$50. SUPER SPECIALS. Bulk Zenith safety capacitors800-860, 12 lot only $2.50 each. REDCOAT ELEC-TRONICS, 104-20 68th Drive, Forest Hills, NY 11375,212-459-5088. 10-82-tfn

REPLACEMENT COLOR YOKES -DEALERS ONLY.Zenith 95-2501-2532-2887 etc. $22.95. Magnavox361380-1 etc. $24.95. Sylvania $24.95. American -madefuses in bulk -example 3AG 2 regular price .23 each ourprice .12 each. Factory packaged GE transistors atdiscounts. Example GE -20 regular price $1.10 ourprice .65. Request circular on your letterhead. DavidSims Enterprises, Inc., 665 East Jericho Tpke., Hunt-ington Sta., NY 11746, 800-645-5030, NY State (516)549-3925-1592. 10.82-tf n

TUBES-Receiving, Industrial and Semi -conductors,factory boxed. Free price list. Low; low prices.TRANSLETERONIC INC., 1365 -39th Street, Brooklyn,NY 11218E, 800-221-5802, 212-633-2800. 5.82 -tin

TV TROUBLE ANALYSIS TIPS. Over 300 symptoms/remedies by circuit area; tough ones over the years.Save time and money. Send $12.50 to CHAN TV, 8151Grandview Rd., Chanhassen, MN 55317, 5-82-tfn

PRINTED CIRCUIT boards from your sketch or art-work. Affordable prices. Also fun kit projects. Freedetails. DANOCINTHS INC. Dept. ES, Box 261,Westland, MI 48185. 5-81-tfn

SONY -PANASONIC -RCA -ZENITH -EXACT REPLACE-MENT PARTS -LARGE INVENTORIES -SEND PART ORMODEL NUMBERS -WILL UPS OR COD -GREEN TELE -RADIO DISTRIBUTORS, 172 SUNRISE HIGHWAY,ROCKVILLE CENTRE, NY 11570. 5 -82 -If n

AUTOMOBILE RADIO and tape replacement parts:Delco, Chrysler, Philco-Ford, Motorola, Panasonic andmany others. Large inventory. Laran Electronics, Inc.,3768 Boston Road, Bronx, NY 10469. (212) 881-9600,out of New York State (800) 223-8314. 5.79-tf

COLOR PICTURE TUBES direct from manufacturer.Prices from $55 to $75 exchange. One year warranty.Send your old tube ups to ATOLL Color Tubes, 6425West Irving Park, Chicago, Illinois 60634. Phone:312-545-6667. We also sell equipment for rebuildingCRT's. 9-83-3t


FOR SALE (CONT.) BUSINESS OPPORTUNITIES

ATTENTION TECH/SHOP OWNERS-Profits gettingsmaller with increasing cost of parts? Take advantageof our buying power and huge inventory on well knownelectronic products and replacement parts. Pricesbelow dealer cost. Write for information. United Ser-vices Assoc., Old Grand Union Shopping Ctr., Rt. 9W,Stony Point, N.Y. 10980, 914-942-2173. 7-83-tfn

CB RADIO BOOKS, kits, modifications. Catalog $1.00refundable. APS, POB 263, Newport, RI 02840. 6-83-12t

SOUTHERN CALIFORNIA SALES AND SERVICEOPERATION available: Over .2 million gross 1982;Thirteen years In area with excellent growth and highvisibility. Audio/Video Sales and Servicenter, 26837Bouquet Canyon Road, Saugus, California 91350,805-255-5562. 9-83-3t

ADVENT VIDEO PARTS and service available fromprofessional electronics. Call 504-467-1717 for furtherinformation. 9.83-3t

FOR SALE: SAMS 900 to 1695, total 300, price $450.CEC P.O. BOX 383, Bellflower, CA 90706. 11-83-1t

RETIRED: Sell or Trade entire inventory TV parts,Modules, Test Equipment, Sams, RCA & Zenith prints.Cost over $19,000, sell $9,500. A. Hudson, 935 CenterAve., Red Bluff, CA 96080 (916) 529-0350. 11-83-1t

COMPLETE SERVICE SHOP. Parts, Sams, Test equip-ment, tools, fixtures for TV, stereo, CB and Radio Service. A turnkey operation, except for van and building.(704) 739-5983 after 6 pm. 11-83-1t

INDIVIDUAL PHOTOFACT FOLDERS (not sets) under#1200. First class postpaid $3.00. Loeb, 414 ChestnutLane, East Meadow, NY 11554. 11-83-3t

WANTED

WANTED FOR CASH: 50, 53, 6AF6, 6HU8, 304TL,4CX1000A, 4-1000A, all transmitting, special purposetubes of EimacNarian. DCO, Inc., 10 Schuyler Avenue,North Arlington, New Jersey 07032. Toll Free (800)526-1270. 5-82-t f n

PHOTOFACTS WANTED. Numbers 900 to 1100. LBTelevision, 326 Kingston Avenue, Brooklyn, NY 11213.

11-83-1t

TELEVISION SERVICE SHOP in Florida or California.Call or write ATOLL TV, 6425 West Irving Park,Chicago, IL 60634; Ph. 312-545-6667. 11-83.3t

BUSINESS OPPORTUNITIES

NORWALK, CALIFORNIA ESTABLISHED TV ANDSTEREO SERVICE AND SALES very busy moneymaker, excellent location, low rent, very good lease,2300 square feet, 10 minutes to beaches and LosAngeles. $40,000 Includes inventory, large enough forliving quarters, owner retiring, phone 213-863-1919.

11-82-tf n

SPEAKER RECONING: Most makes, sizes, models.For prompt service send to Mercury Speaker Recon-ing, 2018 W. Division St., Chicago, Illinois, 60622; (312)278-2211. 9-83-tfn

COLORADO'S WESTERN SLOPE BECKONS:Established R.V. Repair and Sales business. Goodlease, good terms. Century 21 -Old Homestead, JohnMcDermott, 737 Horizon Drive, Grand Junction, Colo.81501 or call (303) 243-5100. 10-83-2t

RESIDENTIAL SECURITY ALARM sales are explodingand the Rampart Associate Program offers you ENOR-MOUS PROFIT POTENTIAL PLUS EXCITINGRESIDUAL INCOME. Rampart's success and reputa-tion are a result of a total business format approachfor the residential, small commercial market and itsnew low cost system, the Rampart REACTOR, withcentral station monitoring. We provide product,marketing and management training with completebackup. Start part time, full time. No experiencenecessary; just a strong desire to succeed and helpyour customers. Investment only $2,850. With only 6%of the market penetrated, now's the time to getyourself started in what Time Magazine calls the"runaway growth Industry." Call Mr. Roberts1-800-823-8002 or write, Rampart Ind. Inc. One OxfordValley, Langhorne, PA 19047. 11-83-tfn

LEARN TO REPAIR HOME VIDEO GAMES IN YOUROWN SHOP! Did you know that more than 9 millionHOME VIDEO games have been sold? Now you canlearn to repair! Atari, Coleco, Intellivision, or Atari400/800 computers in your own shop. Our courses aretaught on VIDEO TAPE (Beta or VHS) and come with amanual containing all the necessary technical infor-mation you will need to do repairs. For more informa-tion or to order, call: Electronic Institute (800) 221-0834(outside N.Y.) or (212) 377-0369 (in N.Y.) Customizedlive in shop training courses are also available, call formore information and price schedules. 7-83-tfn

10 YEAR ESTABLISHED TV SALES and SERVICEBUSINESS (service equipment included) with TV ren-tal business in same building. Excellent downtownlocation with 2000 sq. ft. floor space, side service en-trance, new parking lot being built. Owner will helpfinance and assist initial operation of store. Call207ó96-4242. 11-83-1t

TV TUNER REBUILDING BUSINESS, LOS ANGELES,CALIFORNIA 23 years same location, other interests,requires sale very reasonable, (213) 342-4745. 7-83-tfn

TELEVISION SHOP LIQUIDATION: All parts, shop andoffice equipment for sale. Send "stamped envelope"for parts lists. Samar TV, 8 Dusk Dr., Centereach, NY11720. 11-83-1t

HELP WANTED

SR. VIDEOTECHNICIAN

Pentax Corporation, headquarteredin Denver, has an employmentopportunity for a Sr. Video Techni-cian. This senior position includesactual hands-on servicing of variousvideo products and electronic sur-vey instruments. Also will includecontrol of service production, pro-viding work direction and trainingtechnicians plus performing admin-istrative duties.This opportunity requires extensiveelectronics experience (3-6 yrs.)with previous video servicing expe-rience desirable. Formal electronicstraining is required plus expe-rience in administrative processes.The position also requires goodcommunications skills for cus-tomer service.If you are interested in this chal-lenging opportunity, a competitivesalary and benefit package, pleasecall for additional information orsend resume to:

PENTAXPENTAX CORPORATION35 Inverness Drive EastEnglewood, CO 80112

(303) 799-5212Equal Opportunity Employer

tv&rodiotech's guideto pricing

Everyone benefits...pricing by "The Book"

1-800-228-4338MON. TORO FRI. 8-5 / C.S.T.

ReaderServiceNumber

PageNumber

28 Active Electronics 6025 All Electronics Corp. 5721 Automated Production

Equipment 4918 B&K Precision 4515 Chemtronics, Inc 3916 Components Express, Inc. 41

34 Consolidated Electronics,Inc 64

29 Cook's Institute of ElectronicsEngineering 60

7 The Cooper Group 931 Dage Scientific Instruments 6027 Dandy Manufacturing Co. ..5919 Digitron Electronics Corp...47

ETA 5826 Electronic Specialists, Inc. 595 John Fluke Mfg. Co., Inc 5

33 Fordham Radio Supply ....61General Electric Co.

Television 3723 High Tech Marketing Co 5730 Jensen Tools, Inc. 60

4 MCM Electronics 1

NATESA 58NESDA 62

11 North American Philips 1924 Oelrich Publications 5912 Omnitron Electronics 21

20 Optima Electronics 4736 ORA Electronics 43

1 PTS Corp. IFCPhilips ECG 17

22 Primefax 4917 Projector -Recorder Belt

Corp. 41

RCA Distributor & SpecialProducts Div 7,27

9 Howard W. Sams & Co. ....1332 Satellite TV Week 602,3 Sencore BC37 Simpson Electric Co 2314 Soltec Corp. 2810 Sony Corp. of America 1513 A.W. Sperry Instruments,

Inc 2535 Sperry Tech, Inc . 63

TCG/New-Tone Electronics,Inc 26

8 Winegard Co. 11

Zenith Radio Corp IBC



FREESHIPPING

& HANDLING If order is 5 lbs. or less,good only in the continentalU.S. with purchase of $75or more.

2SD 712SIMILIAR TO ECG® 152

39¢1-800-543-3568

NATIONAL WATS

705 WATERVLIET AVE.,DAYTON, OHIO 45420SORRY. NO MIXED QUANTITIESMINIMUM ORDER $10

2SC1172BHORIZONTAL OUTPUTTRANSISTORSIMILAR TOECG® 238

CEIWI isVll)r./CtOCJ Electronics,

knaorrOfritedCircle (34) on Reply Card

s)ma

FREET-SHIRT

With order of $75 or morn

2SB 682SIMILIAR TO ECG® 153

45¢1-800-762-3412

OHIO WATS

IN DAYTON, OHIOCALL 252-5662

* THESE ITEMS ARE FOR 10 OR MORE

e

11.83

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BUSINESS REPLY MAILFirst Class Permit No. 1810 Overland Park. KS

Postage Will Be Paid By Addressee

GIGOTROAIOServicing &Tee c o'71

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Product InformationP.O. Box 12951Overland Park, KS 66212-9981

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GIGOTRODICServicing &,,Product InformationP.O. Box 12951Overland Park, KS 66212-9981

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The how-tomagazineofelectronics.. .

... bringsyou currentinformationon:

Satellite TVROElectronic GamesMicrocomputersAudio ProductsVideo ProductsTest Equipment*Security ProductsParts. Tools &

Accessories

New technologyand servicedata in everyissue

Plus how-toarticles withmore chartsgraphs picturesand schematics

SUBSCRIBENOW!

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DüWt touchthat connection!

New Zenith push-button VIDEO ORGANIZER permitsswitching from one program source to anotherwithout changing cable connectors. Permits selection of upto six different program sources for viewing. Up to three different sourcesfor recording. Even lets viewer watch one program source while recordinganother. All this withoutchanging cableconnections!

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Model S10W

Pt last the nuisance of changing cable connections byrand is a thing of the past)

With Zenith's new Video Organizer, separate input and out-put jacks facilitate a complete connecticn of TV and VHF;LHF antenna or cable TV antenna, subscri3tion TV decodery deo disc player, video cassette recorder, video game anchome computer or other auxiliary video equipment.

So videophiles switch from one programsource to another with push-buttonease - without changing connections. FM/TN

JCR RECORD -I

E L E C T R O h 1 CNOIVIE VICE()() R O A N 1 2 E R

ZENITH

10.8" wide, 2 7" high, 728" deep

Equally importai=, the Video Organizer's advanced engi-neering design by Zenith results in low insertion oss andhigh isolation. Eliminates electromagnetic interferencefor maximum picture quality And permits greater flex-ibility in use and ease of operation for more hours ofuninterrupted home video enjoyment.

Write now for more information and thename of your Zenith distributor so you

can start cashing -in on the fastestgrowing segment cf the TV business'

Th=_ quality goes in before the name goes on.°

Zenith Radio Corporation/Service, Parts & Accessories Division/11000 Seyrrcur Avenue/Franklin Pa -k, Illinois 60131

SENCORE MODEL SC61 WAVEFORM ANALYZER

Double Your Troubleshooting and TestingProductivity ... Or Your Money Back!

Six -digit readout: Auto-matically tracks everyCRT test. We call itdigital autotracking.It's patent pending.

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Bright dual -trace CRT:60 MHz(-3dB); 100MHz (- 12 dB).

Delta PPV, Time, Freq:Measure any part of awaveform for PPV,time or frequencyusing Delta measure-ments. Just dial in thewaveform sectionyou want to measureand push.

Simplify Freq ratio tests:Automaticallycompare input/outputratio of multiply/dividestages from 1:1 to1:999,999 with thepush of a button.

B Ef-J CD RE MODEL SC61

The first scope with push buttondigital readout. If you use generalpurpose oscilloscopes for trouble-shooting or testing, we can doubleyour present productivity with theSC61 Waveform Analyzer, the firstinstrument to turn every conventionalscope measurement into anautomatic digital readout.

No more graticule counting.Connect only one probe to viewany waveform to 100 MHz. Then, justpush a button to read DCV, PPV,frequency and time - automatically!

There are no graticules to count orcalculations to make, which speedsevery measurement.

The digital readout is from 10 to10,000 times more accurate as well.

Plus you have everything you wantto know about a test point, at thepush of a button, which speedstroubleshooting tremendously.

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WAVEFORM ANALYZER

A special Delta function even letsyou intensify parts of a waveform anddigitally measure the PPV, time orfrequency for just that waveformsection.

And it's neat. No more tangledleads, piles of probes or danglingcords. The SC61 is an entire teststation in one unit.

The one and only. There are otherscopes with digital readout, but noneof them completely automate everyconventional scope measurement soyou can automatically analyze anywaveform without counting onesingle graticule. Totally automaticwaveform analyzing at the push of abutton. It will make all the differencein your productivity.

Double your productivity. Whenwe say the SC61 will double yourproductivity, we're beingconservative. We've seen cases of

U.S. Patent PendingFinancing Available

Autotracking DCV, PPV,Freq: Measure DCV to.5%; PPV to 2%;freq. to .001 %. Justpush a button foreither Channel A or B.

One probe input: Oneprobe input perchannel for allmeasurements -digital and scope -

ith 5 mV to 2000 Vmeasuring range. (2lo -cap probesprovided.)

Super sync: ECLprovides rock -solidsync trigger circuitswith only 4 controls;includes TV syncseparators for videowork.

three, four, even ten time increasesin productivity with this first -of -its -kind, automated oscilloscope. Everysituation is different, however, so trythe SC61 and judge for yourself.Here's our offer.

Money back guarantee. If theSC61 does not at least double yourproductivity during the first thirtydays, you may return it for a fullrefund, including freight both ways.

Call today. Get the entire SC61Waveform Analyzer story. Call toll -free today, and ask for our eight pagecolor brochure. It could be the mostproductive call you make this year!

Phone Toll -Free1-800-843-3338Alaska, Hawaii, Canada andSouth Dakota call collect(605) 339-0100

3200 Sencore Drive, Sioux Falls, SD 57107

For Information Circle (2) on Reply CardFor Demonstration Circle (3) on Reply Card

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