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Red Screen of DeathQuick & Simple Repairs #65Understanding Diodes andTransistors

Gremlins in an Atronic Titan

August 2010Slot Tech Magazine

Randy Fromm's

Slot Tech Magazine

EditorRandy Fromm

Technical WritersDean Auger, James Borg,

Vic Fortenbach, ChuckLentine, Kevin Noble,

Herschel Peeler, Pat Porath

Slot Tech Magazine is publishedmonthly bySlot Tech Magazine1944 Falmouth Dr.El Cajon, CA 92020-2827tel.619.593.6131 fax.619.593.6132e-mail [email protected] the website at slot-techs.com

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Copyright 2010 under the UniversalCopyright Convention. All rights re-served.

Slot Tech Maga-zine

August 2010

Inside Slot Tech Magazine

Page 4-EditorialPage 6-Gremlins in an Atronic TitanPage 10-Red Screen of DeathPage 16-Quick & Simple Repairs #65Page 20-Understanding Diodes and TransistorsPage 26-Subscription Form

Randy Fromm

Randy Fromm - Publisher

Printed back issues are available for only six months from the date of publication. All single issues of SlotTech Magazine are $10.00/ea. For further details on the contents of each issue, please refer to the websiteat slot-techs.com. To order, fax a PO or e-mail a note listing the issues you need.Complete archive (2001 to present) available online. Visit slot-techs.com for details.

Dear Friends of Slot Tech Magazine,

TechFest 21 is coming! TechFest 21 is coming!

Our host for the event is the Sky Ute Casino, lo-cated in the “Four Corners” area of the USA, whereArizona, New Mexico, Utah and Colorado all meet.You can fly into Durango, Colorado (only 7 milesfrom the casino with a free shuttle so you don’tneed to rent a car) but it’s a beautiful drive fromanywhere in California, Arizona or New Mexico.

I have added a new session to the mix of seminars.In addition to presentations on bill validators, ticketprinters, power supply repair and LCD repair, I haveincluded a new session on discrete components thatwill really help novice technicians speed through alltypes of repairs.

Here’s the deal: Knowing how something works andbeing able to repair it are two, almost completelydifferent things. Once you know how to recognizethe parts are and how to test them, you are well onyour way to fixing all kinds of casino electronicswithout having an in-depth knowledge of electronictheory. When you leave TechFest 21, you WILL beable to repair power supplies and LCD monitors,down to the component level.

Slot Tech MagazineAugust 2010


Slot Tech Feature Article

Tracking down inter-mittent problems canbe frustrating, time

consuming and downrightmiserable. We had anAtronic Titan lock up withsix different error tilts.Now, they just didn’t ap-pear out of thin air. Thislock up occurred directlyafter the pull team wentthrough the floor. Thetechnician started with theobvious (as Bill Validatorerror was on the list) andfollowed the switch andwiring to the fuse protectedboard in figure 1. Ofcourse, there were no obvi-ous areas of concern.Checking the fuses, hefound that the 5 amp, 250volt fuse was blown.

Of course this made therepair quite simple. Run-ning to the shop and re-placing the fuse broughtthe game right back on lineexcept for one small issue:The game error codes all

Gremlins in an Atronic Titan

cleared except for GameFamily Error. Well, it hadbeen quite some time sinceI have had to RAM clearthis type of game but aftera quick review, it went quite

smoothly. After the RAMclear, I began to set thegame options. Then wecame to the part of set upwhere you use your donglewith the laptop and com-plete the settings for the

printer, denom, percenthold, etc.

Well, it had been solong, our floorlaptop had beenupdated and our

By Dean Auger


program was still on floppy disk. Wewere able to find an older pc andmove the program to a thumb drive.Surprises just didn’t stop there. Theold program was not compatible withWindows XP and of course, that iswhat we are currently running in allsystems. So now I’m on the phoneplacing the order and processing allnecessary paperwork to expedite therepair, as this is one of our popular“Big Bertha” style machines.

The new version came the followingday, the RAM clear was now com-plete and the game was up andrunning. Until the count team camein again. Now the game was downagain. The same fuse was checked. Ithad blown again. Voltage testsdidn’t detect any abnormalities andwe could not trace anything from theValidator to that board. As you seein figure 2, the bundle of wire com-ing out of the door was quite large.We were running out of areas tosearch. We finally located theshorted light board behind the glass.

Figure 3 shows where the connectorat the solder point on the boardcame loose. When the door wasopened and closed, it had justenough movement to short out andcreate the problem. Although it hadappeared for the first and second daythat we had a bad fuse, the verysimple repair was actually quiteelusive. This was a fine example ofusing the KISS method of trouble-shooting to find the problem. Withthe number of boards that are hid-den behind glass and metal plates,and wires going into large bundles ofspaghetti, it was difficult to locatebut with a little patience and a lot ofpersistence we brought this repair toa successful conclusion.

Dean [email protected]

Figure 1

Figure 3

Figure 2



AVP 2.5The “Red Screen of Death”

Every once in a while,do you ever get thatone game that is just

a pain in your butt? Alemon, I would call it if itwas a car. I was lookingthrough the MEAL book totry to determine when thisproblem first started to be apain in our sides when Inoticed that this one loneAVP game has been a prob-lem child since it first ar-rived. Constant rebooting(over an extended period oftime) and, according to theMEAL book, it kept hap-pening through softwareupgrades and percentagechange RAM Clears. Thiscontinued to happen overthe short life of this game.Just recently the “Redscreen of Death” startedappearing, but just beforethat, the game would ac-cept some bills and, de-pending what kind of moodit was in, freeze up. Basi-cally the entire contents ofthis game had beenswapped out. It was sug-gested from another sitethat they had had the same

Red Screen of DeathBy Kevin Noble

problem and that theyreplaced the boot chips. Noharm in trying as this gamewas getting progressivelyworse. Once the boot chipsarrived and they were in-stalled. I signed out a floatand was a little hesitant toinsert my first bill (it isusually a lot of paperwork ifthe game locks up and youneed to be paid out) butwent ahead anyway. Themachine accepted without aproblem, so did all of therest of the bills. The finaltest was when I actuallyhad to play the game andcash out. Again, without ahitch.

IGT S2000King Cash Mystery ProgressiveGame out of Sequence

Tim Robinson from Clintonhad seven out of eightmachines on the “King ofCash” mystery progressiveworking properly. Theeighth machine on the loophad an “issue.” It keptgoing on its own, being outof sequence with othergames. It would go cyclethrough a routine where itshowed the flying scene,then reset back to thebottom level, then it comesup with the others for

about 10 seconds and re-turn back into the sameroutine. Tim had to rebootit and others tried differentpower supplies. Tim statesthat they also tried a unitfrom another machine. Itwould work fine, they


would replace the card inthe board, and the addresscomes up 8 on reboot like itshould, but still not stayingin sync with the others.When a small JP was hit,the attendants stated theduck is not flying throughthe small screens on thegames but only the largemonitor in the sign. Theproblem ended up that hehad to replace the PCBMonitor board behind theMonitor where the videocard goes in. It must havebeen faulty from the start.The first time the “King ofCash” bank sequencedproperly was after hechanged out this board.Great job guys thanks forthe information.

Bally AlphaNo Progressive ControllerMikohn.1 Error Could NotClear

This is one of those timeswhen the saying “if youdon’t use it, you lose it”comes into play. You see,we were checking the pro-gressive values on allstandalone games usingthe PSP program and thelaptop. About the thirdgame in, we wanted toverify loading and sendingthe progressive figures intothe CHAM II board. When Iproceeded to close the topbox I did notice the pro-gressive display was goingthrough all of its settingand the game startingdisplaying “No Progressive”error and suddenly thetransmit and receive lightswent blank. I wondered if

maybe I had groundedsomething out or pinched awire when closing the case.I verified the game optionswere correct and even wentso far as to swap out theCHAM II board but when Iclosed the door, the errorappeared. I was stumped tothe point that I called MikeSutton, our Bally Rep. Thefirst thing he asked me waswhat version of PSP I wasusing (It had to be over3.0)and was F8 was set toMS25? I told him that I wasnot sure and I would check.I went into the sensitiveroom and discovered that Iwas using a 2.x version andthat F8 would only go to 22.You see, we recently hadour old laptop replaced witha newer version so I had todo a search to find the PSPon the computer. Therewere many PSP icons tochoose from and I guess Ipicked the first on in mysearch. I researched thecomputer again, open it upand verified the version wasover 3, loaded the valuesfrom the CHAM II, changedF8 to 25 and the messagedisappeared. Mike ex-plained to me that the F8defaulted back to MS08when using the old versionPSP program. I had forgot-ten all about the newchange for the Bally Alpha.I even checked my notesand I had the changesmarked in RED so that itwould stand out whenreferencing that informa-tion but who would havethought it would havechanged just from loadingit from the CHAM II and

sending it back. I did re-member checking each andevery F8 from that point on.Thanks Mike, for the re-fresher lesson.

AVP 2.0Operating System UpgradeWill Not Take

Our AVP 2.0 games stillused the installation CD toload into the hard driveuntil this new upgrade wasdone. It will now allow us touse the AE011027 USBexcept for this one gameanother tech was working


on. It started out loadingreally slowly. We almostfinished our two games tohis one. When he finallyreached the Key Chipmenu, the monitor (so wethought) would not allow usto select the KEY CHIPmenu. You see, the touch-screen was off just enoughto hamper selecting thescreen options, or was it?The first couple of times wethought that it was selectedbut once the gamerebooted, it was all fornaught. So, we would startthe process again just toget to the same point. Wedecided to swap the moni-tor with the game beside itbut with the same results.We now decided that wewould start from scratchand wipe everything cleanand start anew. When weselected to wipe out thecabinet memory, the gamejust sat there. The 0%would not move as if thegame was frozen. Wendell,our IGT regional represen-tative, was on site andsuggested that we swap outthe motherboard. Weswapped out themotherboard and replacedthe CPU, rebooted thegame, and the touchscreenwas now working correctly,the Initial set-up worked,and the RAM clear processalong with selecting theKEY CHIP menu all workedallowing us to set the op-tions and ticket test thegame.

CVT #20EPROM Error & Returnedto Normal Status Messages

Well, here is a new messagebeing displayed on theTPE_RPT log that I havenever seen in all the yearswe have had the EZ Paysystem. I was wondering ifthis was only displayedbecause of the games beingAristocrat or since we justupgraded the U70 and U83EPROMS last week. It allstarted around 9:30 AMjust after we opened to thepublic (go figure) whenmanual jackpots and tick-ets not validating at thewindow reared its uglyhead. This is not the firsttime I have written aboutthis same CVT or thegrouping together of IGTS2000 (COMM Board) orthe Aristocrat (fiber board,SPC II boards, or the fiberpower supplies) machinesall on the same loop. It’salso funny how we haveother Aristocrat gamesscattered throughout thefloor with the same modeltypes but never a problemlike we have with this onebank of ten machines. Westarted looping out aboutfive games at a time to see ifthe error messages wouldstop.

We had a call from someonewho was monitoring the logwhile we were out trouble-shooting the problem. Afterreading the log and lookingfor clues to see what couldbe bringing the systemdown, one IGT S2000 stood

out more than the rest. Wedecided to start there bychanging out the Commboard. That seemed to slowdown all the messages butthe problem still existed onthe first two Aristocratgames coming from the CVTroom. We started loopingout the back side of theAristocrat games when allof a sudden, the problemstopped. We figured it hadto be one of the gameslooped out. We startedlooping back in one gameat a time and the problemdisappeared. We really didnothing for it to stop. Justabout lunch time the prob-lem started up again. Westarted the troubleshootingprocess again. This time welooped out the first twoproblem games according tothe TPE_LOG and startedlooping out five games at atime until we went aroundthe bank and ended upback to the back side of theAristocrat bank again.Then, unfortunately, ourshift was about to endwhen we relayed everythingto the afternoon crew.When I arrived first thing inthe morning it was broughtto my attention that we hadno problems with theTPE_LOG and everythingwas up and running. I hadto open up the Tech shiftreport to see if the solutionwas posted and it was.Afternoons looped out poll#3 (the third game on theloop) and the problem wentaway. They stated that with#3 looped out, they pro-ceeded to swap out all thefiber boards on the Aristo-

TechFest 21October 12-14 2010


crat bank as a precaution.They lastly replaced thefiber power supply on poll#3 and looped the gameback in and the problemdid not return all night.Checking the TPE_LOGfirst thing this morningconfirms that the problemwas gone. Great job guys!

Konami VideoCD ROM Error

That was the error beingdisplayed on the screenwith two games left in thebonus round. First wethought that the CD ROMwas bad until we startedswapping it out with aknown good one fromanother game but theproblem remained, thenfrom the Vidmar cabinet inthe shop same problem butdifferent codes. We wouldget different errors all thetime, the red “diagnosticerror,” the constant reboot,blank screen for minutesand back to the CD ROMread error. Nothing wasconsistent. We swappedharnesses, power cables,power plugs, slim line CDROMs and the plain tanthick CD ROM drive. Oncewe had the machine gothrough the verificationprocess, the CD passed,the graphics loaded andthen it froze. We figuredsince the CD ROM pluggedinto the CPU the only thingwas to shut it down untilAGCO could come in andbreak the seals to the CPU.I had some free time thenext morning so I decidedto go over to the game,

power it back on and spenda couple of minutes on it. Ipowered up the game, itwent through its internaltesting, loaded the sounds,loaded the zip. File from theCD and came back online.The game played its last twobonus games, cashed outthe ticket so it can bevoided. The game has beenup ever since with no prob-lems. And that day was notFriday the 13th.

Aristocrat VideoMachine Options Changed

Another interesting mes-sage on the TPE-log wasbeing displayed on theterminal that needed to beinvestigated. When we re-moved the top glass on thegame, the SPC II board lost

power. We touched theboard and the LED startedblinking again. We startedchecking the three “J”connectors and found therewas a short in the harnessat J3 connector. When youpushed on the slidingdrawer in the top box, thiscondition would happenagain. When the harnesswas replaced, the errorswent away.

- Kevin [email protected]

TechFest 21Sky Ute Casino

(Four Corners USA)October 12-14 2010

$495 per personIncludes Breakfast & Lunch



Konami Reel Tilts

A call was receivedthat an uprightKonami game was

having quite a few reel tilts,specifically reel 2. I hadreceived a call for reel tiltsin the same area a coupleof weeks ago so I had to tryto remember what I did torepair the problem. It tooka few minutes and I remem-bered. A couple of weeksago, a Konami uprightgame in the same area hada lot of reel 3 tilts so thereel was pulled out of thegame to be examined.When looking at the reeloptic and optic encoder,there was A LOT of dustbuilt up. It was very obviousthat the dust was the prob-lem. An optic emits aninfrared light and whenthere is so much dust builtup on it, the light can’tpass through properly. Areel was removed from the

Quick & Simple Repairs #65By Pat Porath

game and obviously therewas a lot of dust in theoptic area. I used com-pressed air and a Q-tip toclean the area and put thereel back in the game. Ifone reel optic has dustbuild up on it, the othertwo probably do too so theother two reels were re-moved, and the opticscleaned on them as well.Within a short time, a cus-tomer was playing the gamewithout any problems.

IGT Trimline LCD Problem

We had an IGT Trimlinegame that had a distortedmain LCD. Why not startout by checking the videoconnections to make surethey are nice and secure?When wiggling the VGAconnector on the LCD, thepicture would become clearso it looked like the LCDhad a component internallythat was possibly goingbad. Also, when the unitwas tapped on, sometimesthe picture would becomeclear. Off to the shop tolook for a spare. We hadtwo so I grabbed one. Dur-ing the installation at thegame, first I plugged in thevideo cable, then the USB

touch screen cable. What?Where is the darn USBsocket? To my surprise theunit I grabbed didn’t have atouch screen on it. You mayask why wouldn’t it haveone? Well, on a Trimlinegame, the upper LCDdoesn’t use one. Back tothe shop again to grab theother spare and this onedid have a touch screenport. After installing thisone in the game, it looked


like it had a power problem.There wasn’t any sign ofpower at all. On the side ofthe LCD there is a smallLED on the remote boardthat is supposed to light upwhen power is applied. Itdidn’t.

Now what? Why not takethe back off the originalLCD and check it out? Witha little luck there would besomething obviously wrongand maybe I could repair it.The large back cover wastaken off, then the smallerone that covered the videoinput board. To my sur-prise, the video board alongwith the LCD power supplywere a bit loose. A quickcheck of all the connectionswas done too but all I couldsee was the two looseboards. After both weretightened down, the coverswere put back on and the

LCD was put back into thegame. Awesome, I fixed it.Possibly the boards had abad ground from beingloose or it was just an FMrepair.

IGT AVP Kept RebootingItself

While a co-worker wasdoing conversions, I wasasked to look at an AVPthat kept rebooting itself. Ifit would fully boot up and,after some time, wouldreboot, then I would say ithad a bad video card. Thisgame would not boot up allthe way before rebooting.Being that the game hadbeen on the floor for awhile, maybe a couple ofyears or so, we thought thepower supply may be bad.It was replaced, and theproblem still persisted. Toverify that the power supply

was good, we swapped itwith a known good workinggame and it was in fact agood one. I thought maybethe game had a softwareproblem because of the newchips that were installed. Iremoved the Brain Box andchecked them out. Theylooked like they were in-stalled correctly and noneof them had any bent pinsthat I could see. Otherchips were examined to seeif they were loose and theconnectors were checked tosee of they were loose too.The ribbon cable connectorthat comes from the gamehard drive and plugs intothe board was a bit loose. Itwas pushed back into thesocket and the rest of theconnectors were checked.Now we’ll see what hap-pens. Power was turnedback on for the game andthis time it booted up per-


fectly. It must have beenthe loose ribbon cable thatwas causing the problem.

IGT S2000 with a NetplexError

I had an IGT S2000 thathad a Netplex Error on theVFD that didn’t want toclear and the gamewouldn’t boot up. Also,there wasn’t any voltage onthe reels. In my past expe-rience, it looked like a badpower supply. After gettingone from the shop andputting it in the game, theproblem still existed. An-other weird thing I noticed,the LEDs on the VFD driverboard weren’t lit. Manyconnections were checkedbut nothing appeared to beout of the ordinary. Themain processor board wasexamined. It looked like itmay not have been pushedall the way in. It wasreseated and the power wasturned on once again. Thistime I did have LEDs on thedisplay board and the gamelooked good. The processorboard must have comeloose just enough to cause

problems. Another gameback online.

Oasis Dim Display Prob-lem

On the gaming floor,we mostly have Senti-nel IIs and some Senti-nel IIIs. The displayproblem was on aSentinel II type. Mostof the time, if the dis-play is very dim, theSentinel is rebooted orthe display is replacedand it is fine. It wasn’tthe case this time. Irebooted the Sentinel afew times withoutsuccess along withreplacing the displaybut the problem stillremained. Next, Ichecked the cable andmade sure all of thewires were pushed intothe connector properly.Still no go. A sparecable was installed andas soon as power wasapplied, the displaylooked good. It was simply abad cable.

- Pat [email protected]

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Tuesday, October 12, 20109:00 am - 12:00pmElectronic Component Testing Presented by Randy FrommElectronics repair is actually pretty easy, once you know how to testthe components. It often doesn't matter if you know how somethingactually works in order to fix it. You just look for bad parts and replacethem. This seminar covers all of the discrete components thatcommonly fail in slots. We'll look at how they work, how they fail, andhow to test them fast and easy.

1:15pm - 3:15pmMEI - BV troubleshooting and repair

3:30pm - 5:30pmFutureLogic Printers-Suzo-Happ's Director of Training and ServiceDavid Oldham will discuss MEI and FutureLogic operation and service.

Wednesday, October 13th, 20109:00 am - 12:00pmPower Supply Repair Presented by Randy FrommLet's face it, we have a lot of pwer supply failures in slot machines.Some power supplies are more-or-less disposible due to their cheapreplacement cost but many of the supplies we find in slot machinesare custom-built units costing hundreds of dollars. We will cover theoperation and repair of power supplies in detail during this session.

1:15pm - 3:15pmLCD Monitor Repair Presented by Randy FrommLCD monitor repair is easy. This is the first of two presentations onLCD monitor repair at TechFest 21. During this seminar, we will coverthe theory of operation of LCD monitors and you'll see just how simplethey really are. We will also cover circuit analysis of the electronicswith an emphasis on what fails and how it can be repaired in anycasino's tech shop.

3:30pm - 5:30pmIncredible Technologies-Incredible Technologies has been creditedby many operators as one of the most important and innovativemanufacturers of video games in the world. Now, IT brings their teamof manufacturing and design experts to the casino industry and toTechFest 20 with a close look at their IT slot machine.

Thursday, October 14th, 20109:00 am - 12:00pmCeronix LCD Monitor Repair-Although it can be argued that all LCDmonitors are more-or-less the same, it's nice to get the inside track onspecific monitors from the manufacturers themselves. Ceronix's HeadTechnician Troy Nofziger will present.

1:15pm - 3:15pmTransact Technologies-Transact Technologies' Russ Wigé presentsservicing and troubleshooting Transact brand, thermal ticket printers.These units are simple to understand and troubleshoot, once youknow how they're put together.

3:30pm - 5:30pmJCM Bill Validators-This is arguably the best seminar of its kind inthe gaming industry so we've saved the best for last. This presenta-tion will be given by JCM's Jack Geller. This is your chance to ask theworld's #1 expert about your JCM "issues."

Schedule subject to change

Continental breakfast and full lunch servedeach day. Students are responsible for theirown transportation, lodging and evening meal.


Slot Tech Classic Electronics

Do you rememberwhen you firststarted working on

slots? Remember when youdidn’t even know what atransistor was, let alone howto test one to see if it wasgood or bad? Now that you’vebeen working on power sup-plies and monitors for awhile, you probably can’t re-call a time when you didn’tknow how to test transistorsand obtain substitute com-ponents.

If you can call to mind thedifficulty of those early days,you’ll understand why I oc-casionally take a step backand take a look at some ofthe fundamentals of trouble-shooting. Of these basicskills and procedures, noneis more important than theability to test transistors. Ifyou are already familiar withtransistors, this discussionwill probably be a completebore. Consider yourself for-tunate to possess such a vi-tal skill and move on in themagazine. I’ll catch you nextmonth.

Still here? That’s good be-cause you just gotta learnhow to test transistors. It’s re-ally the whole basis fortroubleshooting monitors,power supplies, drivers fordiverter coils and a host ofother things electronic.

The basic philosophy is

simple. Since many circuitfaults are caused by transis-tor failure, we don’t alwayshave to know exactly how thecircuit works in order to re-pair it. All we have to do istest the transistors in the cir-cuit and replace the onesthat are bad. Since transis-tors all test the same (with afew exceptions) once you’vemastered the test you can fixjust about anything!

Diodes

We use the “diode test” func-tion of the meter to test bothtransistors and diodes. Let’stake a quick look at diodesfirst.

The diode is the simplestsemiconductor that we have.The schematic symbol lookslike an arrow with a bar atone end. The arrow symbolmakes a lot of sense since adiode is a one way gate forthe flow of electric current.It’s kind of like the turnstileat a supermarket or amuse-ment park where people areallowed to move through thegate in one direction only. Adiode has just two compo-nent leads. They’re called the“anode” and the “cathode.”

It’s interesting to note howthe diode actually works in-side. Just about all of the di-odes we use in games aremade of an element calledsilicon. In its pure form, sili-

con is an insulator. It can-not pass any electric currentthrough itself. During themanufacturing process,small quantities of impuritiescalled dopants are added tothe silicon. The addition ofthe dopants causes a changein the structure of the sili-con atoms.

When phosphorus is addedto the silicon crystal, extraelectrons are added to thesilicon. This gives the silicona net negative charge, withsome free electrons scootingaround inside the crystal. Wecall this type N silicon; N fornegative.

When boron is added to thesilicon, it develops a net posi-tive charge. We call this typeP silicon. We can think oftype P silicon as having at-oms with “holes” in the elec-tron shell, just waiting for anelectron to fall into it. In fact,we call these atoms in thetype P silicon “holes.”

The diode is made from asingle chip of silicon. Onehalf of the chip is type P sili-con; the other half is type Nsilicon. Where the two typesof silicon come together, wehave something called thePN junction. The PN junctionacts as a kind of barrier toprevent the free electrons inthe type N silicon from reach-ing the holes in the type Psilicon. When we test diodes

Understanding Diodes and Transistors


and transistors, we will ac-tually use the meter to testthis PN junction. Your abil-ity to test this PN junctionwill enable you to repairmore electronic equipmentthan any other single testyou will perform!

It takes a certain amount ofvoltage to push aside the PNjunction and allow current toflow through the diode. Ittakes an average of .7 volt tobreak down the PN junctionand allow current to flow.

Let’s hook up this diode andsee how it works. The anodeis connected to the positiveside of the battery. The cath-ode is connected to the nega-tive side of the batterythrough the lamp. The elec-trons are repelled by thenegative side of the batterytoward the junction and theholes are repelled by the

positive side of thebattery toward thejunction. Where theymeet at the junction,the electrons fall intothe holes. This pushesthe PN junction asideand current flowsthrough the diode.

If the battery is re-versed, the holes andelectrons are at-tracted to oppositeends leaving pure sili-con as an insulator betweenthem. The silicon insulatorprevents current from flow-ing through the diode. Thisis why it is called a semicon-ductor. Sometimes it con-ducts; sometimes it doesn’t.

It takes around .6-.7 volt tobreak the barrier at the PNjunction. This .7 volt is usedup inside the diode as the en-

ergy required to push thecurrent across the PN junc-tion. We call this .7 volt the“JUNCTION DROP.”

A normally operating silicondiode will have a JUNCTIONDROP of between .4 and .8volt when measured withmost digital multimeters.Most engineers and techni-cians use the average of .7


volt when discussing theJUNCTION DROP. Generallyspeaking, the larger the de-vice, the lower the JUNC-TION DROP will be. We cantest this JUNCTION DROPwith our meter. There is aspecial setting on the metercalled the diode test. Whenwe use the diode test, we areactually measuring the volt-age required to get throughthe PN junction. What weshould see is a normal JUNC-TION DROP with the red leadon the anode and the blacklead on cathode (diode con-ducting) and OPEN when theleads are reversed.

This means that the diode isdoing its job as a one waygate for current. When weread a normal JUNCTIONDROP it means that currentis flowing through the diode.When we read OPEN, the di-ode is blocking the current.

It’s obvious when a diode isbad. If we get a reading inboth directions, the diode isshorted. In fact, most diodesshort when they fail. I’d saythat 99 out of 100 diode fail-ures are short circuits. If themeter shows OPEN in bothdirections, the diode is open.

You can usually tell if a di-ode is good or bad, evenwhen testing diodes in-cir-cuit. Needless to say, if youtest a diode in-circuit and itappears to be bad, youshould test it again after re-moving it from the circuit justto be sure.

Diode Specifications

A diode is rated by voltageand current. The voltage rat-ing of a diode is the maxi-mum amount of voltage thatthe diode can block withoutbreaking down. The voltagerating is listed as PRV (peakreverse voltage) or PIV (peakinverse voltage.)

The current rating is them a x i m u mamount of cur-rent that the di-ode can safelypass withoutgetting too hot.Believe it or not,we use the letter“I” to representcurrent. Huh???Early experi-m e n t e r sthought of cur-rent as “inten-sity,” so the let-ter designation“I” has remainedwith us. Iomeans outputcurrent.

When substitut-ing diodes, youcan always use adiode with ahigher voltageand/or currentrating. Remem-ber, the voltagerating of a diodehas nothing todo with the volt-age the diode is“putting out.” Itis simply a rat-ing of the maxi-mum voltagethat the diode

can block. You can replace a50 volt, 1 amp diode with a400 volt, 1 amp diode. Youcould also use a 50 volt, 3amp diode or even a 400 volt,3 amp diode as a replace-ment.

Transistors

Transistors come in a lot ofdifferent shapes and sizes.The packages we commonly

This is the smallest transistor thatyou commonly will find in moni-tors, power supplies and othercircuits (other than SMDs or sur-face-mount devices). It is oftencalled a "signal transistor" as itcan handle only 1 amp of current.

This package can handle upto around 10 amps. We usetransistors in this package inpower supplies and manyother applications.

The TO-218 (and other,s imi lar packages wi thplastic tabs) package is alarger version of the TO-220 package. It's used inmany of the same applica-tions as well.


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see in games are TO-220, TO-218 and TO-92 but there aredozens of others as well..There are two polarities oftransistors: NPN and PNP.Both are named for the waythey are made. They’re kindof like a sandwich with typeN and type P silicon. Theschematic symbol for the twotypes of transistors is basi-cally the same. Notice thatthe arrow points away to des-ignate an NPN transistorwhile the arrowhead pointstoward the center of theschematic symbol for PNP.

Since we’re talking a lotabout P’s and N’s here,chances are pretty goodwe’re talking about a PNjunction somewhere. In fact,each transistor has two junc-tions. The NPN transistor ismade of a single chip of sili-con that has one area madeof type N material, a thinnerregion made of type P siliconand another N region on theother side. The PNP transis-tor has N silicon in themiddle, surrounded by P sili-con. These are technicallyknown as “bipolar transis-tors.”

A transistor has three leadsand each lead has a name.They are the emitter, base,and collector. There are twoPN junctions in the transis-tor that we have to test. Oneis between the base and theemitter. The other is betweenthe base and collector. It isthe same test we used forthe diode but we’ll check twojunctions instead of just one.

TESTING TRANSISTORSRegardless of what type ofpackage they’re in, transis-tors will pretty much all testthe same way. You’ll need adigital multimeter with a “di-ode” test.1. Set your meter to the di-ode test.2. Connect the red meter leadto the base of the transistor.Connect the black meterlead to the emitter. A goodNPN transistor will read aJUNCTION DROP voltage ofbetween .45v and .9v. A goodPNP transistor will readOPEN.3. Leave the red meter leadon the base and move theblack lead to the collector.The reading should be thesame as in step 2.4. Reverse the meter leads inyour hands and repeat thetest. This time, connect theblack meter lead to the baseof the transistor. Connect thered meter lead to the emit-ter. A good PNP transistor willread a JUNCTION DROP volt-

age of between .45v and .9v.A good NPN transistor willread OPEN.5. Leave the black meter leadon the base and move the redlead to the collector. Thereading should be the sameas in step 4.6. Place one meter lead onthe collector, the other on theemitter. The meter shouldread OPEN. Reverse yourmeter leads. The metershould read OPEN. This isthe same for both NPN andPNP transistors.

If the transistor fails any ofthese tests, it is bad. If youread a short circuit any-where, the transistor is bad.As with the diode, you mayattempt to test transistors in-circuit. However, transistorswill often not test properly in-circuit and must be unsol-dered and removed from thecircuit for proper testing.Don’t agonize over whetheror not the transistor is badwhen testing in-circuit. It


only takes 30 seconds to re-move the transistor and an-other 30 to test it properly.Just do it!

Transistor Specificationsand Replacements

Transistors are rated muchthe same as diodes; maxi-mum current and maximumvoltage.

IC- Collector Current - Thisis the maximum current(measured in amperes) thatcan be controlled by thetransistor. Naturally, largetransistors can handle morecurrent that small transis-tors, just as thick wire canhandle more current thanthin wire. The largest sizetransistor we commonly usein games is the TO-3 pack-age, which can handle up to40 amps of current.

VCEO or BVCEO - Collector-to-Emitter Voltage - This is themaximum voltage that thetransistor can handle asmeasured between the col-lector and the emitter whenthe base lead is open (notconnected.) This is when thetransistor is completelyturned off and must blockthe current from flowing be-tween the collector and emit-ter of the transistor. Althoughthere are other voltage rat-ings for transistors, this isgenerally the only one that’simportant to us.

hFE - Current Gain or “Beta”- This is an indication of thetransistor’s ability to amplifyan incoming signal. Thehigher the gain, the less cur-

rent it takes to drive the tran-sistor. For example, a tran-sistor with a gain factor of100 will require just 1/100amp of base current for 1amp of collector current.

We can lump most transis-tors into three general cat-egories. Low gain transistorshave a gain of up to 250. Me-dium gain transistors have again of 250-750. High gaintransistors are those with again factor of more than 750.Admittedly, these figures aresomewhat arbitrary.

Substituting transistors isjust like substituting diodes.You can make the substitu-tion as long as the replace-ment transistor is the samepolarity (NPN or PNP) andhas the same or higher volt-age rating and current rat-ing.

However, you should try tomatch the gain rating of thetransistor as best you can.Substitute only low gaintransistors for low gain tran-sistors, mediums for medi-ums and highs for highs.This is not actually too diffi-cult. As long as you’re in theballpark you should be okay.

Naturally, if you can obtain

an exact replacement youshould do so. Most citieshave at least one electroniccomponent retailer who car-ries a series of universal re-placement components thatcan be used as substitutes.These companies publish anextensive cross-referencecatalog that will allow you tomake substitutions asquickly as locating a word inthe dictionary. You simplylook up the original partnumber of the componentyou want to replace and theindex will tell you which sub-stitute to use.

A cross-reference is alsoavailable online from NTE.http://www.nteinc.com/.You can download theircross-reference database aswell, making it possible foryou to cross-reference com-ponents without having to beon-line. - STM

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