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Inside Slot Tech Magazine

Slot Tech Magazine

Inside Slot Tech Magazine

Slot Tech Magazine

December, 2001December, 2001December, 2001December, 2001December, 2001

Page 2 - Editorial

Page 4 - Slot Doors and Slot GodsA closure error that may suprise you

Page 8 - Mikohn's Casino LinkKevin Noble introduces us to Casino Link in part one of a two part series.

2 - Suicide in SENetDigital repair is, well, er . . . Logical!

Page 18 - TechFest II InformationEnrollment form for the January 9th - 11th event. For Slot Techs Only!

Page 20 - That Feeling of RejectionCoin rejection can be caused by many things

Page 24 - Dion's CornerCoin-In Time Out, confused buttons and More

Page 26 - Low Voltage Equals High BrightnessUnderstanding the relationship between cathode voltage and electron gun emission

Page 28 - Understanding Linear Power SuppliesPower supply failure is commonplace.Learn how they work in part one of this two part series

Page 36 - Subscriptions and Back IssuesOrder form

IGT showed State Fair atthe Global Gaming Expo.The game's artwork gracesthis month's cover.

Slot Tech Editorial

Randy FrommSlot Tech Magazine December, 2001

Randy Fromm's

Slot Tech Magazine

EditorRandy Fromm

Technical WritersPete Bachran

John GreenBart HoldenKen Locke

Kevin NobleJake Olson

Herschel W. PeelerScott Reynolds

Frank Sutter

Advertising ManagerDennis Sable

Slot Tech Magazine ispublished monthly bySlot Tech Magazine1944 Falmouth Dr.El Cajon, CA 92020-2827tel.619.593.6131fax.619.593.6132e-mail

[email protected] the website at

slot-techs.comSUBSCRIPTIONS

Domestic (USA) 1 year - $60.00 2 years - $120.00International 1 year - $120.00 2 years - $240.00

copyright 2001 under the Uni-versal Copyright Convention.All rights reserved.

Randy Fromm

If this month's Slot Tech Maga-zine had a title, it would be Warand Peace, not for any rel-

evance to the War on Terrorismbut for the length of some of thismonth's articles. Two of them hadto be split into two parts each andthey're STILL long. But that meansdetail and in my book, that's good.Anyone can spout vague nonsenseabout slot repair. The devil is inthe details so when you look at thetable of contents and see fewer ar-ticles, you know why.

Happy Holidays to all and bestwishes for a prosperous and happynew year ------------------------

Dear Randy,

I was hiredthree monthsago as a SlotTech at theSpirit Moun-tain Casino inMohave Valley,Arizona, a smallTribal casino.

I’ve learned alot in a shorttime and I want to learn more. I’ma retired air traffic controller and Ihave a strong background in me-chanics, administration, and writ-ing skills. My weakness is elec-tronics ( Re: the article by FrankSutter in the November issue). Itook a yearlong course in radioshop in high school in the early1960’s. A lot has changed sincethen.

Thank you for sending me two is-sues of your Slot Tech Magazine.While I’m not totally familiar withall the terms yet, they were veryinformative and interesting. I par-ticularly liked the articles aboutCommon Machine Problems, Solu-tions and Repairs by Kevin Nobleand Slot Tech Electronics 101. (Ireally needed the refresher)

Performance and Politics alsocaught my eye. I have no desire toenter that arena, having been anair traffic control supervisor andmanager for over ten years.

I was impressed by the contents ofSlot Tech Magazine and the lim-ited amount of superfluous adver-tising. Your articles were informa-tive, direct and to the point.

I am enrolled in your seminar inLas Vegas on Jan 9-11, 2002 and Ilook forward to meeting you andyour Tech Writers.

The Slot Tech field seems to offera fantastic opportunity for newpeople that want a respectable ca-reer (I am one) and a good stablejob.

See you next Year.May God bless America,

George Feick

Hi, George,

Thank you for your nice commentsabout Slot Tech Magazine. I am gladthe articles have been helpful to you.I’d like to point out to you that theadvertisements in Slot Tech Maga-zine are far from superfluous. Tradejournal advertisements in this or anyother trade journal serve to informreaders of new products and servicesas they become available. How elseare you going to find out about thisstuff?

On the practical side, subscriptionsalone cannot cover the expenses ofadministration, production, printingand distribution of a monthly peri-odical such as Slot Tech Magazine.Through their continued support, ouradvertisers assure that we can con-tinue to provide technical training andsupport to the industry’s slot ma-chine technicians.

I look forward to meeting you at Tech-Fest II in January. Your badge andother material has been sent to you.

That's all for this month. See you atthe casino.

Slot Tech Magazine December, 2001

Slot Tech Feature Article

PROBLEM-No door closuresignal on IGT slant top poker

SOLUTION-Faulty powersupply

Last month I was involvedin a slot machine movethat involved relocating

ten IGT players edge plusslant top poker games. Ofcourse there isn’t a whole lotto this move. You disconnectthe power and the playertracking harness and trans-port the slot machine to itsnew home. Next you recon-nect the power and playertracking and the machine isready to be refilled and cointested. Apparently I left out astep according to a few of ourgames non-conforming be-havior.

Once the games had beenmoved the whole five feet,two had a door open thatwould not clear. Of course Iwent straight for the dooroptics. I could not use diag-nostics due to the fact thatthe Central Processing Unit,CPU, was locked in a CMOSfailure. My dog ate my in-

frared tester leaving me nochoice but to replace the op-tics without verifying theiroperation. Oh wow, the nobrainer didn’t fix the prob-lem. I opened the awardglass door to check the billvalidator cherry switch andit was also good.

I decided to take the CPU tothe tester in the shop andsee what would happen. Thegame recognized the doorclosure and I was able toclear the CMOS error. Thegame played properly andeliminated the CPU as theproblem. On my way out ofthe shop, I grabbed the digi-tal multimeter and a sparemotherboard just in case.

Once I arrived at the game Ibegan to take continuitychecks with my meter fromthe optics to the motherboard.I also checked the wiringfrom the bill validator cherryswitch. They were all faultfree. In the back of my mindthoughts of the motherboardbeing faulty were causingme to develop the shakes. Ididn’t particularly want toremove and replace it. I havedeveloped a phobia of remov-ing motherboards all be-cause of those Williams slanttops. I need counseling butthat is another article titled“Handle Mechanisms, Monitors,and Motherboards Sent Me ToThe Nut House”.

I then took a very deepbreath and unlocked and re-moved the CPU. I detachedthe seven connectors fromthe motherboard and re-moved the three screws andturned it this way and thatway until it finally broke free.That wasn’t so bad. Once re-moved, I studied themotherboard carefully look-ing for a burned trace orsome sign of hope that Iwasn’t barking up the wrongtree. Everything looked to befine and since looks can bedeceiving, I opted to replacethe motherboard with thenew one. After a few uncom-fortable minutes of twistingand squirming in the driedstrawberry daiquiri thatsomeone so graciouslyspilled on the floor of thegame, the motherboardwas installed.

I gathered my composureand asked forgiveness for afew adjectives that I hadtossed about during thecourse of my troubleshoot-ing. It went something likethis, “If this works, I promiseI won’t say $#@% again.” Ipowered up the game closedthe door and voila, the doorstill read open.

This seemed like a good pointto open up a working slanttop beside my game and lookback and forth intelligentlyat the two hoping that theproblem would appear to me

SLOT DOORS AND SLOT GODSBy Bart Holden

in neon lights. Once I gotthe feeling that people wereon to me, I grabbed themeter and set it to voltage. Ichecked the voltage to thedoor optics and noticed aslight difference between thegood game and the badgame. On the good game Iread between 7.5 and 8 voltsdc. While on the bad game Igot a reading of approxi-mately 5-5.5 volts dc.

Was this enough to cause thedoor to stay open? I decidedto change the power supply.Luckily we had taken severalpoker slant tops to storagewhen we were moving every-thing around. So I closed allthe games and made thejourney to our temporarystorage facility and began re-moving a power supply. Hav-ing never removed an IGTpoker slant top power sup-ply, I blindly began discon-

necting harnesses and re-moving screws. I removed afew screws and harnessesthat weren’t necessary.However, it wasn’t too diffi-cult but I was surprised tofind that the motherboard isattached to the power sup-ply housing. All in all it re-quired removing about sixnuts and screws includingone ground wire and ap-proximately ten harnesses.

I returned to the floor withmy replacement power sup-ply and a renewed feeling ofconfidence. I removed thepower supply from the faultygame and now knowing whatI was doing, accomplishedthe task in half the time. Iinstalled the new power sup-ply and once again pausedfor a moment of reflectionafter leaving behind someforearm hair in the straw-berry daiquiri that now

closely resembled flypaper.

The moment of truth had ar-rived. Would the slot techprevail or would he onceagain miserably crumble atthe hands of an outdated slotmachine. I wiped the sweatfrom my brow, flipped theswitch and the monitor read,“now power up self-testing”for what seemed like an eter-nity. “Come on, I’m ready tosee if this works.” Finally itwas time for me to close thedoor and I did so and the ma-chine again entered into aCMOS error. This time how-ever, the game received thedoor closure signal and I wasable to clear the tilt with myreset key. The heavensopened and the slot godssang. Actually, I opened theshop door and my slot techmanager sang.

- Bart [email protected]

Slot Tech Feature Article Mikohn’s

By Kevin Noble

I have had great opportuni-ties in my short career intraining new technicians

coming into our department.Starting the new techs off withpolicies and procedures, theninto some sound advice suchas documenting everything inthe M.E.A.L. (machine entryauthorization log) book so it’seasier for the next technicianto solve, always protectingyour rear, and a slot machine isa slot machine, is a slot machine.What I mean by the last state-ment is that once you get to knowhow one manufacturer’s machineworks, the others usually fallinto place: reel tests, hoppertests, limits, and so on.

This is the basic principle Iuse to train new technicianscoming into the department. Ifind this the easiest way.Show them the basics, andthen show them the differ-ences between the othermanufacturers. This is wherethe Mikohn Casino Link comesinto play. I have worked withCDS, SDS, and then intro-duced into Mikohn’s CasinoLink. I applied the other twosystems and the third justcame naturally.

I remember the first time wehad a major problem on thefloor where the SMIB (SlotMachine Interface Board)

went off line on a number ofgames in a bank. I started thetroubleshooting as if I was us-ing the CDS system. I un-plugged half the bank to see ifthe front half came up, thenhalved that until I came to thehomerun and the four ma-chines on a single splitterboard. After unplugging thefour machines and the bank,I started to plug in one gameat a time to see if the gamestarted communicating againor if the game brought the linedown. When the game broughtthe line down, we checked thecommunication chip. It was sohot it burned the tips of yourfingers.

We continued this processuntil we had completed thewhole bank. We found that 18out of 24 games had blown thecommunication chip. I havetold the technicians on myshift that you should now beable to apply the same strat-egy towards the SDS and CDSsystems.

The Mikohn System is beingused all over Ontario, Canada.There are currently manysites throughout Ontariojoined to a central site. Be-cause this system is being sowidely used here in Ontarioand the United States, I wouldlike to expand on this systemfrom a technical point of viewand discuss some of the parts,set-ups, error codes, testcards, LED’s and all the otherstuff that goes along with thesystem so you can see other

systems used in today’s ever-growing and expanding field.So sit back, relax and imag-ine how the saying “a slotmachine, is a slot machine, isa slot machine” could apply tothe different accounting sys-tems used in today’s market.

The Parts

SMIB(slot machine interface board)The SMIB is usually mountedin the Award glass of the slotmachines. The SMIB commu-nicates with DCU (data collec-tion unit), which is locatedsomewhere off the gamingfloor. The SMIB also commu-nicates with the games infor-mation such as meters, dooropens, game tilts, power downsand ups and all the other in-formation that the game cre-ates.

The SMIB also displays suchcodes as “S” codes that areSMIB errors, “M” codes thatare the last machine errors,door open/close, and actualcoin in, out, and drop to allowthe technician to see if themeters increment when test-ing each meter respectively onthe display.

There is a communication linethat connects from the SMIBto the splitter board. This al-lows for the communication tothe system via the SMIB toDCU, DCU to IOC, and thenthe IOC to the central system.The SMIB board has the capa-bilities to disable the machine


Author's Note: On Monday night a tech-nician on my shift had emergency brainsurgery and is currently in a coma herein a Windsor hospital. I would like todedicate this article to him. His name isToufic but we all call him "T." We areholding a fundraiser for him. If you canhelp, please contact [email protected]. I hope you can help. Thanksgreatly. -Kevin


from the central site where itis located. The setting of adipswitch does this. (Seedipswitch settings)

The Machine HarnessThe machine harness linksthe SMIB and the game to-gether. Each manufacturerhas a different harness thatplugs into the game’smotherboard and sends infor-mation to the SMIB. Metermismatch information oftencan be linked to this harness,especially when it becomesnicked, damaged, or has aloose connection. The slotdoor, cash box and drop doorare part of this harness thatconnects to cherry switches onthe machine.

Switches (fill, slot, drop, andcashbox)These switches are used tomonitor the cashbox, fill door,slot door, and the drop door,for entry to the games (espe-cially when the machine ispowered off) for any illegalentry except for employeeswho have access to the ma-chines. This is done throughthe employee’s type 99 cards.

PTM (player tracking mod-ule)In simpler terms, this is thecard reader. The PTM plugsinto the SMIB, to the displayand the keypad.

IOCAn input/output controllerdoes all the handing of thecommunications to and fromthe DCUs and from the cen-tral location. The IOCs polleach DCU in order to collect,store, and transmit data to thefile server. All data collectedfrom the floor is received fromthe DCUs. The DCUs sendand receive data from the in-dividual slot machines on the

floor. The DCUs poll each slotmachine on an individual ad-dress. If the slot machine hasany activity to report, it re-sponds with a packet of infor-mation which the DCU willthen hold in storage until theIOC polls that DCU for thatpacket of information for pro-cessing.

DCU (data collection unit)The DCU transfers data to andfrom the IOC. The DCU cancontrol 4 lines coming fromthe floor, with up to 31 gameson each line. The DCUs aremounted on racks in a sepa-rate room with the IOC off thegaming floor. Each line that isconnected into the DCU hasits own transmit and receiveLEDs that blink when data isbeing transmitted and re-ceived. The DCU itself has oneset of transmit and receiveLEDs, which communicatewith IOC. Also, there is onered LED that represents the“heartbeat” of the entire DCU.This also blinks when theDCU is powered up.

Splitter BoardThe splitter board uses 6 po-sitions for the bank in, orhomerun coming on to thefloor (#1), four communicationlines (#2 to #5), and the bankout (#6). This can be mountedanywhere in the base whereit will not be damaged by bagsof coins or drop buckets. Thesplitter boards are usuallydaisy chained together de-pending on how many gamesare in each bank.

DID (Dallas id)A unique, hexadecimal ID ad-dress that will be assigned toeach game. The DID is neverthe same for any game andcan only be used once. TheDID connects to the SMIBboard and will be displayed

first when the 99 card is firstinserted. The DID numberalso will be displayed whenthe game loses communica-tion with the SMIB or DCU.This ID number must be en-tered into the system beforethe SMIB board will commu-nicate with the DCU.

Cabinet or RackThe cabinet contains the IOCand a file server. The rackusually houses the DCUs aswell.

Introduction

99 Card(usually the employee card)The 99-employee card allowsthe employee access into themachine without triggering analarm to the surveillanceroom when the slot door, filldoor, cashbox, or drop door isopened or closed. When the 99card is inserted into the PTM,the display will cycle throughdifferent values starting withthe DID number (in hexadeci-mal format) along with theDCU address that was as-signed to that unit. The fol-lowing information follows: thegame type setting that is usedset by the SMIB’s dip switches,the coin in, out and drop, theSMIB version EPROM, theROM version, the PTM version,and then the bill log metersstarting from 03 that repre-sents $5.00 to 07 which rep-resents $100.00. Here inCanada we no longer have the$1.00 or $2.00 bill.

98 (Technicians Test card)When the 98-test card is in-serted into the PTM, the dis-play will show a single screenthat represents the state ofthe doors, “M” error code, “S”error code, and three 0’s thatrepresent the coin in, out, anddrop movement. The “1” rep-

Slot Tech Magazine Slot Tech Magazine December, 2001

resents the coin in, “2” repre-sents coin out, and “3” repre-sents the coin drop. Eachsingle digit will increment upto 9, and increments when asingle coin is inserted,dropped, or paid out. Themeter will not increment thenumber of coins, but changesstate to show the technicianthat the meters are working.The “M” represents the lastmachine error reported, the“S” represents the last SMIBerror reported, from left toright slot door, drop door andcash box door. The “0” meansthe door is closed and “0”would change state to “1” totell us the door is open. Tocheck for communication, the“S” would turn into a “B1” thattells us the game is commu-nicating and “B0” telling usthe game has lost communi-cations with the machine.Another thing to think aboutwhen using this card is thefact that it does not allow en-try into the machine withoutsounding an alarm, and thatsetting dip switch 8 to the onposition and resetting theSMIB (unplug the power andreconnect), allows you to con-duct the test sequences withthe doors, and coin tests with-out the 98 card inserted.

SMIB BOARD LEDs

1. Power indicator – red– steady when theSMIB has power

2. Transmit – green- litduring transmission

3. Heartbeat – red –blinks off/on whileSMIB software is run-ning

4. Receive – green – litduring receiving

5. DCU transmit not –green – off when theSMIB is transmittingmessages to the DCU

6. DCU transmit – green– lit during transmis-sion

7. DCU receive – red – litduring receiving

SMIB Board DIP Switch Set-tings

DIP #1 to #4 -Assigns what kind of commu-nication protocol used for asystem or game type setting- Example- IGT SAS 2 and 3on, no game type- 1, 2, 3, setto off,DIP #5- Is used for ROM SIG verifi-cation-On tells the SMIB not to dis-able the game-Off allows the game to be dis-abled from a central site.DIP #6-This allows you to enable thediagnostic ports; it must be setto the on positionDIP #8- Allows to get into the door,coin meters, and error codesto be displayed.

The IOC Processes

The IOC is essentially a com-puter that runs a certain setof processes in order to trans-mit and receive informationfrom various slot machines viaa SMIB board and DCU. TheIOC must at least run the firstthree processes:

Pipe manIt creates pipes to communi-cate with other processes. Italso routes messages to andfrom various processes.

MconfigThis maintains the addressconfiguration and machineproperty information for ma-chines specified on the IOC.It is also responsible for the

DCU time requests.

SyscommIt is used to control communi-cations between the DCUsand the IOC. When it receivesa message from the PIPE MAN-AGER, it sends it to the properDCU, and when it receives amessage from the DCU, itsends the message to thePIPE MANAGER.

Player TrackingIt receives messages from theSMIBs when a player insertsor removes their card.

AlarmsIt handles alarm messagesthat are received within thesystem. These consist of door,DCU, and SMIB errors.

FillJackIt routes hopper empty andjackpot messages from thefloor to the screens in thecage.

Points SchThis communicates with thePlayer Tracking process to ad-just the point bonusing for-mula.

IOC Power Fail Procedure

Problem: When a whole DCUgoes down, the red “receive”light on the DCU will notflicker at the high rate ofspeed. You can notice the dif-ference when watching anyother DCU lights. The bottomlone red lights are for the IOCtransmit and receive. Thelight is noticeably slower. TheDCU will constantly show“POLL OFF” and whatever ison that DCU on the floor willshow the large hexadecimalnumber from the DID. Whenthis happens, a power fail isneeded to bring each channel


on the DCU back on line oneat a time. The procedure forthis process is as follows:

! Unplug all channels onthe DCU.

! Click on each processand close the file byclicking the “X” in thetop right hand corner.Continue this sequenceuntil all processes arecompleted or closed.

! Press control + alt +delete

! Click on log off, the sys-tem will start to log offthe network.

! Press control + alt +delete to log back on

! Type in the usernameand password

! Click on the icon “IOCPOWER FAIL” and theprocesses will comeback on line.

! At this time you canplug in one channel andwatch the status of thechannel. The channel’sreceive red light shouldbe flickering as fast asthe others.

! After watching the sta-tus of the channel, thestatus will read on theDCU x, 0,0. The “X” rep-resenting the numberof games on that chan-nel. The next “0” repre-sents “0” are down, andthe next “0” represents“0” are missing. If allgames are present onthe channel, continueon to the next channelby plugging that in.

! After all channels andDCUs are running, thenext step is to close allthe processes downagain quickly, and clickback on the IOCCASINOLINK.

! This actually brings all

the processes back online and gets the sys-tem running again tofull capacity.

! This process can takefrom one-half up to anhour to complete de-pending on the play onthe floor and the databeing received by theDCU and the IOC.

! Remember, every per-son and/or site hastheir own way or proce-dure to do this. Pleasecheck into your ownpolicies and proce-dures.

DCU Ram ClearThis process is used as a lastresult if the DCU is taking toomuch time to come on line.This process clears all thedata that is stored in the DCU,which slows the dumping ofthe packet of information tothe IOC. The meters are notlost, only the player points forthat time the DCU is down. Inconjunction with the IOCPOWER FAIL procedure, pro-ceed to do the following:

! Power down the DCU! Remove all channels

from the DCU! Unplug the battery back

at J2! At J2 short the battery

connection with a smallscrewdriver by touchingboth pins

! C9, C10, C11, and C12also must be shortedwith a screwdriver

! The battery connectorcan be placed back onto J2

! The power switch canbe turned back on.

! Begin to plug one chan-nel in at a time in theabove process, makingsure each channel’s

status is up and run-ning before plugging inthe next.

Terminology

SMIB- receives data from thegame, processes it, and sendsit to the DCU.

DCU (Data Collection Unit)-sends and receives data fromeach game on the floor to theIOC.

SYSCOMM PROCESS- con-trols communication betweenthe DCU and IOC, also sendsmessages to the correct DCU.

MCONFIG PROCESS- housesthe addresses and machineproperties

MCONFIG PROCESS (CAGE)-controls all the fill and jack-pot requests

PROGRESSIVE LINK PRO-CESS- controls the contribu-tion percentage for the coin inand the games.

PLAYER TRACKING PRO-CESS- player’s services, playercards, ECT.

ALARMS PROCESS- all ma-chine entries, jackpots, lostcommunications, power fails

CASINOLINK DATA BASE (ONSERVER) – records data usedfor process, displays, reportsfor accounting, and playertracking.

In part 2, we'll look at trouble-shooting and provide you witha list of real world symptomsand solutions.

-Kevin [email protected]



As your hawk-like gazescans the gamingfloor searching for fail-

ures, a feeling of confidencesettles into you. This is yourdomain, your jungle. Yourule as a benevolent dictator.Surely, there is nothing youcan’t handle.

There, ahead in the distance,near the showroom you spot

a flashing candle. Instinc-tively, you spring into actionto quell the chaos. Whenyou arrive, the S2000’svacuum fluorescent displayreads “coin-in sequence er-ror.” A sardonic grin blazesupon your face. You knowwhat to do.

You deftly open the maindoor and inspect the coin-inassembly for obstructions.Finding none, you reseat thedoor I/O card. “That shoulddo the trick. Goddamn, I amgood.” You close the doorwaiting for the tilt to clear soyou can return to yourthrone of technical power.

Nothing. “Oh yes, of course,it must be the other I/O card.Yet another bumbling floor

attendant has loosened it.There, that should definitelydo it.” You close the dooronce again, and…. Nothing.No reset, no reel spins, nolights.

“Ok, no problem” you thinkto yourself. “I read Slot TechMagazine. I can fix this.”Last month's STM saidknowing your self-test diag-nostics is the key. You startwith Door I/Os and headstraight to the coin in. Youattempt to toggle the opticswith a coin. Nothing. Thenyou test coin-out, thenswitches and lights. Stillnothing. Your confidence isslipping and now a smallcrowd gathers. The pressureis on. What do you do?

Suicide in the SENetBy Ken Locke

Slot Tech Magazine

Okay, I have beat this color-ful scenario to death, sowhat’s the answer, already?It’s simple. Simple periph-erals to be precise. To knowwhat that means, it’s time tohead back to the shop anddig out the dust-coveredschematics and find out. It'stime to explore the secrets ofthe SENet.

For this conundrum, we’llneed the IGT publicationElectronic Diagrams &Parts, Vision Slot Upright,p/n 821-296-01. If youdon’t have a hard copy, youcan get it online throughwww.igtproducts.com.

Taking a good hard look atour problem slot, we seethat we have lost coin-in,coin out, switches, incan-descent lights and thehandle solenoid. The prob-lem is widespread and mostlikely has a common de-nominator. Logic dictateswe go directly to where it allbegins, in the main proces-sor.

Find the processor boardschematic and identifyU721, the SENet chip. Getyour reading glasses out forthis, the print is miniscule.

So there it is. This inte-grated circuit controls all thesimple peripherals in andout of the processor. Thequestion is, which ones andhow? First, it is importantto examine the definition ofan Input and an Output.

In the simplest terms, an in-put is any signal that goes

into the processor. Similarly,an output is a signal that issent out of the processor.Now that we know that, wecan surmise that the list of“gozintas and gozoutas” ispretty lengthy. It must takea fairly sophisticated systemto handle all of them. That’swhere the SENet comes in.

The Synchronous Expansion

Network (SENet) is a serialcommunications channel forsimple I/O devices; Simpleinputs that report an “on” or“off” or 1 or 0 and outputsthat produce an “on” or “off”or 1 or 0. They’re just dumbanimals, simple switchesthat are either in a high orlow state. Examples of com-plex peripherals would be thebill validator, touchscreen


controller and VFD. Theseare microprocessors in andof themselves and communi-cate with the processor on amuch higher level, but that’sanother article.

The SENet can handle 256inputs and 256 outputs. Itworks in direct conjunctionwith the I/O cards. Each ofthese cards handles sixteenindividual peripherals and wecan plug up to 16 I/O cardsinto the SENet or 16 X16=256. This covers the “ex-pansion” part of this chip.How about the “synchro-nous” part?

Let’s go back to the sche-

matic. In the upper left, wesee a series of signals. Putthe tip of your pencil on theone identified as “SENCLK”.This is the SENet clock. Atypical clock signal in anysystem has one primary job.It keeps time. It is the drum-mer in the Simple PeripheralBand.

The SENet works by address-ing each individual board insequential order. It sendssignals to the first I/O card,handling the first output,then the first input associ-ated with that board, thensecond output, then second

input and so on until all 16

inputs and outputs havechecked in. It continues tothe next board dealing withits inputs and outputs in thesame way.

In this way, the outputs fromthe processor are latchedonto the I/O assembly dur-ing the rising edge of theclock. Inputs from the I/Ocards to the processor arecommunicated during thefalling edge of the clock.

Outputs, tick. Inputs, tock.

The SENet processes each of

the sixteen boards, zerothrough fifteen, whether theboard is physically presentor not. So even if we remove,say, the coin comparatorcompletely, it does not haltmachine operations.

Follow the SENCLK signalout to Pin 10b of J1. We canassume, for the moment,that this line is headed to theI/O cards.

Looking at the Lower Cabi-net I/O board (Figure 2) AtJ51 we find SENCLK on pin2. It is dispersed through-out the circuit to J52 (Fig-ure 3.) and we get a look atthe simple peripherals asso-ciated with this board.

This can also be said of theDoor I/O board (see figures4 and 5). The clock makesits appearance on J40, pin 2(gozinta!) and out to periph-erals on J41 (gozouta!).

The beat goes on and this

Figure 2. Lower Cabinet I/O board

Figure 3. The simple outputs


SENet clock is key to thewhole thing. But like spot-ting an Adam’s Apple on yourprom date, you get the feel-ing there is something justbeneath the surface thatyou’re not seeing yet.

Take another look at yourmachine. You’ve lost yoursimple ins and outs. Anotherthing that’s missing is theseven-segment display. Thequestion is, what does losingthe SENet devices have to dowith the seven-segment dis-play? After all, it was noteven listed on the pin-out ofeither of the I/O cards. Forthe answer, return to theschematic.

On the lay out for the seven-segment circuit, notice J51.Merry Freakin’ Christmas!Right there on pin 2 is ourlittle drummer boy. Theseven-segment display, for allintents and purposes, is aSENet device. Once more,you feel the power of slotknowledge seep into yourveins.

And now, here’s the reasonyou read this mag in the firstplace. What you can’t findin any manufacturer’smanual is that all of thesetroubles originated here. U8(found just to the right ofJ51) appears as a series of

triangles called inverters. Itis this component thatcauses our catastrophic fail-ure and is the inspiration forthis article.

U8, known to many techs asthe “suicide chip,” is highly

Figure 4. Door I/O board

Figure 5 - Door I/O

Slot Tech Magazine

Are you a slot tech with something to say? Do youhave some special technical tips you'd like to sharewith your fellow slot techs around the world? SlotTech Magazine is read by slot machine technicians,slot managers and engineers in Argentina, Australia,Canada, Cyprus, Germany, Gibraltar, Ireland, Korea,Mexico, New Zealand, UK, Japan, Saipan, South Af-rica and casinos across the US. For writer's guide-lines, visit the website at slot-techs.com

susceptible to hot swapping,specifically as it pertains tothe coin comparator. Insome casinos, I won’t men-tion any names (but they’rein Atlantic City) it is stillstandard operating proce-dure to put a machine out ofservice by disconnecting thepower harness on the coinmechanism. Since it workson unstable AC power, theold S-Plus holds up nicely tothis abuse. However, thenew Visions and S2000s arewusses in comparison.

Basically, by hot swapping itsends a power spikethroughout the SENet andthis U8 chip takes it on thechin and shunts our clock toground. The result: none ofthe simple I/Os can talk tothe processor. Additionallythe “meters disconnected” or

“coin-in sequence” messagecomes up because this is onething to which the programcan react. No clock equalsno meters or coin-in, whichcomes through as this tiltmessage.

Swap out the seven-segmentdisplay board and order toyour kingdom is restored.Once again, you are DaBomb.

As this incredible year comesto a close, I would like to ex-

press my sincere gratitudefor your readership and yourletters. Things in our worldwill never be the same and Ithank the Big Guy that youand I are still here. Enjoyyour holidays; hug your kidsjust a little harder and here’shoping the best of your pastwill be the worst of your fu-ture.

- Ken [email protected]


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Wednesday, January 9th, 2002

9:00 am - 12:00pmHow Monitors Work - Part 1Theory of Operation - Beginninglevel

12:00pm - 1:00pmLuncheon sponsored by:Happ Controls

1:00pm - 3:00pmAsahi Seiko - Coin hopperconversion, troubleshooting andrepair.

3:00pm - 3:30pmAfternoon Coffee Break

3:30pm - 5:30pm3M Touchsystems / MicroTouch- Touchscreen Technology

Thursday, January 10th, 2002

9:00 am - 12:00pmHow Monitors Work - Part 2Narrow Down the Problem -Intermediate Level

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3:30pm - 5:30pmCoin Mechanisms, Inc. - CoinComparitor technology andrepair

Friday, January 11th, 2002

9:00 am - 12:00pmHow Monitors Work - Part 3Circuit Analysis and Compo-nent Level Troubleshooting -Advanced Level

12:00pm - 1:00 pmLuncheon - Sponsored by MedecoHigh Security Locks

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By Frank Sutter

One of the more common faults that atechnician will face on

the floor is coin rejection. Theprocedure for dealing withthis problem is quite simple,and for that reason, it needsto be done in the most expe-dient fashion possible. Thebest way for the new techni-cian to insure that he canconsistently put this prob-lem behind him quickly is todevelop a plan that will effi-ciently cover all common pos-sibilities. It should go with-out saying that, as soon asyou find evidence that sug-gests the cause of the prob-lem, you should drop the pro-cedure and address your sus-picions.

First, remember that themachine itself will reject coinsby design whenever a fault ispresent in the machine. Thisis a feature designed in as acourtesy to the customer andhelps to guard them againstexperiencing needless losses.Yes, it’s true. Customers willtry to play the machine, evenwhen the power is off.

I’ll never forget the time I wasworking on a machine, nearthe power supply. The door ofthe game was open and thepower was off. I had the coin

tray off the game and thehopper was on the floor nextto me. My head was deepinside the lower part of thegame, with barely enoughroom for me, a screwdriverand a flashlight to all fit in. Iwas distracted from my in-tense concentration and dis-comfort by the close-up soundof a dropping coin. Becauseof the amazing acoustics inthe bottom of an uprightgame, I had assumed thatsomeone was playing thegame next to me. I heard itagain and then somethinghit my leg. I gave my leg aquick glance and saw anotherquarter bounce off.

In sheer disbelief (and at therisk of giving myself a concus-sion) I pulled my head out ofthe machine to look throughthe reel glass of the opendoor. I came face to face witha man who looked nearly assurprised as I was! He hadanother coin in his hand andhe was ready to drop it! Hereally thought he was goingto play. When I popped up inthe reel glass, he must havethought he hit the ugly jack-pot! I tried my best to keep astraight face while I explainedto the man that the game wasbeing worked on and wouldbe down for a while. Then I

snagged a few quarters fromthe hopper to hand to himand he shuffled off into thecrowd without a word. I’m notsure how many quarters Ihanded him but I had nodoubt that he would give themback to the casino in lessthen a minute. Even whenyou’ve been on the floor for awhile, there are still somethings that happen that makeyou shake your head. It’s partof what makes the job so great!

Besides a machine fault, oneof the most common causesfor coin rejection is an elec-tronic glitch in the logic ofthe CPU board. For that rea-son, the first thing that thetechnician should do is toturn the machine off and onagain. If the machine comesback up with a fault still onit, clear the fault and tryagain to insert coins. If coinrejection still occurs, remem-ber that the bill validator alsohas to be functioning prop-erly in order for the machineto accept coins. Glance overand make sure that it is en-abled and ready to play.

If the machine is a Bally,there is usually a switchmounted on the front of theCPU tray that is used to dis-able the coin and the bill

validators. This switch is foruse by slot attendants ifthere is a reason to turn thegame down. I hope I’m notthe only technician who setabout troubleshooting one ofthese games, only to find outlater that the switch was inthe wrong position. I’m surehowever, that I’m the onlyone ever to admit it in print.

If those steps haven’t led youto the cause of the problem,open the door and checkthat the coin validator isplugged in. If there is anyreason at all to suspect theconnections, confirm themby unplugging andreplugging the connectors atboth ends. In gaming juris-dictions that are locatednear the ocean, salt air cancorrode the metal of the con-nection. This process slowlyadds resistance to the cur-rent flow by building a layerof oxidation between the con-tacts of the connection.

Plastic also has a way ofchanging characteristics overtime. Urethane plastics areformed by infusing a chemi-cal resin with a catalyst,which will cause the resin toreact, or “kick” into a plasticform. This reaction continuesthrough the life of the plas-tic, which means that overtime, the plastic will becomeprogressively harder andmore brittle. Both the heatof machine operation and theultraviolet light put off by itsfluorescent bulbs tend to ac-celerate this curing process.If you’ve ever found a pingpong ball that has been outin the weather for a summer,

you will know what I mean.

Through this slow but con-stant process, connectorscan actually loosen them-selves without ever beingtouched. Fortunately, un-plugging and replugging theconnectors will usually solvethe problem. If it does not,visually inspect the connec-tors for looseness or bentpins. Trace the wiring har-ness as far as you can easilysee it, looking for pinched orbare wires. Check carefullyalong the door seam. Thedoor’s hinge can sometimespinch the wiring. Glance atthe connectors for frayingand gently stress each of thewires for possible looseness.

If the connections are solid,remove the validator and ex-amine it. Check for coins ordebris lodged in the coinpath. If the validator requiresa sample coin, make sure aclean new coin is used forthat function. With thevalidator out, visually inspectthe encoder, more frequentlyreferred to as the coin opticchute. The chute comes indifferent sizes for different

denominations and if theencoder is too small, this con-figuration cannot physicallyaccept a coin and count it.On the other hand, if theencoder slot is too large,coins may pass throughwithout being counted. Con-firm that the validator is thecorrect denomination. Try allits moving parts for free mo-tion and no binding.

If the coin path passes visualinspection, the next step isto swap out the validator witha similar unit from a known-good operating machine.While you do this, check thecoin head for proper denomi-nation and confirm that thevalidator lines up with boththe coin head and the en-coder. On slant top games, abent door or even a loosehinge can cause misalign-ment. Make sure that all of themounting posts are in good repair.

The next step is to insurethat the coin validator is get-ting the power it needs tooperate. Remember that thecoin validator is supposed tolose power with the dooropen, so you are going to

The drawing on the left shows the proper encoder for thedenomination of the game. The drawing on the right showsthe wrong encoder, and the coin missing the optics.



have to fool the machine intothinking that the door isshut. The machine monitorsthe door position with a sen-sor, in most cases an optic.On older machines whichuse a cherry switch to sensethe door, fooling the ma-chine is easy! Simply pull outthe cherry switch and thejob is done. On machinesthat use an optic sensor tomonitor the door, there isusually a self-test mode toaccomplish the same job. Bythe way, if the validator ispowered up with the dooropen, on some games this isa hint that there may be ashort in the door wiring. Besure to check the coin opticwiring if you find this situa-tion to be the case.

If you are sure that you arein the door-closed mode andthe substitute, known-good

validator fails to power up inthe original machine, checkthe machine’s 24-volt fuse,and pray that it is blown. Ifthis fuse is good, you areprobably facing a wiring orconnector problem some-where in the machine. If theknown-good validator comeson dimly, check for an over-heated diverter coil.

By now you have confirmedthat the validator works, thatit is getting power and thatit is properly mounted andaligned, so it ought to be ableto accept coins. Grab a hand-ful, throw them in the trayand shut the door. When theinsert coin light comes on,attempt to play the game andsee what the customer mightbe experiencing.

If the acceptor accepts coinsintermittently, some techni-

cians will adjust the sensi-tivity of the acceptor to bemore forgiving. This will getthe game going again, butyou must understand thatthe chances of the game ac-cepting slugs goes up dra-matically when you do this.I do not recommend thistechnique; I simply includeit because I know it's some-times used.

The key to this simple pro-cedure is speed. Since thereisn’t much to this problem,the key is to get through itquickly.

Problems beyond that wouldinclude CPU, I/O or RAMproblems, and will be dis-cussed in the future in thosecontexts. Till next time, keep‘em runnin’

-Frank [email protected]

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Be prepared for six hours of accelerated learn-ing each day. Class begins at 9:00 am sharpeach day and continues until 4:00 pm. The Ca-sino School provides each student with referencematerials and troubleshooting guides that willbe valuable aids for repairing equipment on loca-tion and in the shop.

Students learn how to work with:

THE DIGITAL MULTIMETER This relatively inexpensive piece oftest equipment is easy to operate.Casino School students learn to usethe digital multimeter to perform testsand measurements that will pinpointthe cause of a failure down to a singlecomponent.

ELECTRONIC COMPONENTS The individual components used in games areintroduced. Parts such as resistors, capacitors,diodes, potentiometers and transistors are cov-ered individually. Students learn how the com-ponents work and how to test them using the meter.

SCHEMATIC DIAGRAMS Schematic diagrams are the “blueprints” forelectronics. Learning toread schematics iseasy once you know howthe parts work!

POWER SUPPLIES Power supply failure is a common complaintin many different types of systems.. Powersupply failures are discussed during the class,along with shortcuts for troubleshooting andrepairing them.

MONITOR REPAIR The monitors used invideo slots are designedfor quick, easy, and saferepair. Students will learnthe theory of operation ofall types of monitors and

how to repair monitors down to the compo-nent level. Of course, monitor safety will alsobe discussed.

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Coin-In Time Out?

Here is an interesting problemfor you. You get a call to anIGT Player’s Edge poker gamewith a door open and coin-intimeout tilt. The floor personhas already checked the com-parator and has blown out theoptics and the coin-in tilthasn’t cleared. First, you tryto get the door tilt solved soyou can find the coin-in prob-lem. You check the door op-tics and the BV door to see ifthey are the problem. They allcheck out to be working fine.Well, maybe it’s the fuse. Ifthe fuse checks out good, re-move the CPU and check theresistor packs in the top leftcorner of the board. You’llprobably find that someonehad removed the board and hitit on the chassis. In the pro-cess, they have inadvertentlyremoved RP3. Replace the re-sistor pack and you’ll be backin business.

Confused Buttons

So there is a guest playing apoker game and the floor per-son calls you on the radio andtells you that the buttons arenot working. You arrive on thescene to find out that the but-tons are actually working,they’re just confused anddon’t know which switch they

really are. When you hit the“hold” switch for card numerone, it holds three too just be-cause it thought you reallyneeded that card as well.

This can be a couple of things.First, you could have a badswitch in that circuit or maybethe floor person got in to theproblem a little further thanthey told you and swapped allthe wires around. Afterchecking all the switches andthe wiring, the buttons stillaren’t working. Remove theCPU and check all the diodesin the top left corner. They willbe labeled CR1, CR2, CR7,CR8, CR9 and CR10. You’llprobably find that one of themis smoked. Replace the smokedcomponent, reinstall the boardand hope that it doesn’t smokeagain. If it does, get out theschematic and enjoy.

Scrambled Bally

If you get a call to a Bally andthere is no display or it’sscrambled, you know right outof the gate that it’s a boardproblem. First, try the partialclear then the full clear butthere’s still nothing. You takethe board out and find thatthere is no visible damage.You take the board to theshop, dig out the schematicsand begin a process that couldbe very frustrating and timeconsuming. Where do youstart? Start with U68, whichis an SRAM. Replace it and trythe board in the tester. Ta-da!

Bell Ringer

Here is a real piece of work. Ifyou have these on the floor,get rid of them. Just kidding.I’m sure you have all comeacross the famous 91 F code.No communication to the topunit. No big deal except theydo it all the time. If there is a

permanent fix, let me know (e-mail [email protected]). Anyway, powerdown and open the top box.Open the cover on the CPU inthe top box. Move your jumperfor a partial clear. Try it withthe top box first. If that doesn’tdo it, you’ll have to clear thetop and the bottom together.When doing them together,make certain that the pluggoing into the bottom board forthe top box is unplugged whileclearing. This should clear the91 F. If all else fails, FULLCLEAR. What a wonderfulgame.

BallyGot a coin in problem with aBally and it’s not the compara-tor or the optics? Check theswitch on the board. It shouldbe in the up position.

Another one you might comeacross is a Bally stealingcoins. OPTICS but what on theoptics are bad? It might be theIC U1. I have found that it canbe the crystal Y1 as well. Ifthere is no light on the optics,change out Q3. This is a PNPgeneral-purpose transistor.NTE 129 or 2N4403.

WilliamsI have come across two Will-iams games in the past twodays where the BV drop doorhas come open and when youattempt to close it, will notlatch. Open the validator door.Down by the door switch,there is a bracket. The screwfor this bracket is underneaththe assembly. Remove it toreveal four nuts. Tightenthese and close the door

Bada Bing Bada Boom

Hope to see ya all at TECH FEST

-Dion [email protected]

Dion's CornerBy Dion Anderson


Slot Tech Product SpotlightSlot Tech Feature Article

When does not enoughbecome too much?There are a couple of

interesting monitor failuresthat will cause all three elec-tron guns in a picture tubeto operate wide-open, blast-ing out billions of high-en-ergy electrons and causingan uncontrollibly brightwhite screen with clearly vis-ible vertical retrace lines.

When it comes to the cath-odes of the electron gun, lowvoltage translates into bigemission. That’s right . . . Thelower the voltage at the cath-ode of the electron gun, thebrighter the screen will be.

At first glance, this seemslike just the opposite of theway you would expect theelectron gun to operate. Imean, generally speaking,you squirt some juice into anoutput device and it doessomething. The more juiceyou squirt into the device,the more you get out of it.The higher the voltage on alamp, the brighter it burns.The higher the currentthrough a coil, the strongerthe magnetic field. Greateroutput power from an audioamplifier translates intolouder sound coming fromthe speakers.

But in the electron gun of apicture tube, the emission ofeach gun is modulated bychanging the voltage at thecathode and here, groundingthe cathode will cause theoutput to go to 100%. Try itsometime. Ground the cath-ode of the red, green or bluegun at the CRT socket. You

will see the screen come onfull red, green or blue de-pending on which of thethree cathodes aregrounded.

By the way, this is a quickand easy way to test the elec-tron gun in a CRT. When youare missing a color, yourproblem could be in eitherthe chassis or the CRT. Toquickly determine whichone, try grounding the cath-odes of the cathodes one ata time. You should see abright screen with verticalretrace lines. If you don’t, theelectron gun in the CRT isat fault. This saves a lot oftime.

But what can cause all threeguns to come on full blast?Well, a couple of things cancause this. A simple test ortwo will quickly pinpointwhich one.

One cause is loss of the volt-age to the video output stageson the neck PCB. This volt-age is generally derived froma tap on the primary wind-ing of the flyback transformerin the high voltage unit. Theoutput is rectified and fil-tered to provide a power sup-ply of around +175 to +190volts DC depending on themake and model of the moni-tor. In some monitors, thevideo output stage is pow-ered by the B+.

If this power supply is miss-ing, either through a badcomponent or broken con-ductor, the voltage at thecathodes drops to zero andall three electron guns come

on full blast. I know it seemsweird that a missing powersupply would cause too muchoutput but this is the casewith the electron guns.

If you suspect this is yourproblem, measure the volt-age at the collectors of allthree video output transis-tors with no input signal. Ifyou find the voltage to be lowor non-existent, you MAYhave located your problem. Isay “may” because there isanother possibility here.

The three video output tran-sistors are driven by thevideo amplifiers as we saw inlast month’s Slot Tech Maga-zine. In a modern monitor,an integrated circuit handlesthe job of amplifying all threecolor signals and passes theamplified signal to the out-put stages.

The outputs of the video am-plifier IC typically drive thebases of the output transis-tors directly. They are DC orDirect Coupled amplifiers.What that means is that if theIC fails in such a way that itputs out too much DC volt-age, it will turn on all threevideo output transistors. Infact, the transistors will be“saturated” or turned on ashard as they can be. Whenyou measure the voltage atthe collectors, it will be verylow because the collectorsare now connected more-or-less to ground through just200 ohms or so of resistance.

There are a couple of waysto determine where yourproblem lies. One is to use a

Low Voltage Equals High BrightnessUnderstanding the Relationship Between Cathode Voltageand Electron Gun Emission


meter to measure the powersupply voltage of the videooutput stages. In otherwords, after you’ve checkedthe collector voltage andfound it to be very low, moreyour meter lead to the otherside of the collector resistorand measure the voltagethere. It’s always easy to lo-cate these resistors on anymonitor because they are

three identical resistors andtypically two watts. One sideof all three resistors will betied together and connectedto the video output powersupply. That’s where youmeasure the voltage. If thevoltage is low there as well,you have a problem with yourvideo output power supply.

On the other hand, if the

power supply is good but thevoltage is low when measuredat all three video output col-lectors, your outputs areprobably being over-drivenby a bad IC. An easy checkis to touch the collector re-sistors. If they are really hot,you’ve narrowed down yourproblem.

-Slot Tech Magazine


Modern electronicsuse switching regu-lator or switched-

mode power supplies for awide variety of different sys-tems. They’re used in moni-tors to obtain the B+ powersupply. They’re used as lowvoltage power supplies forslot machines. Of course,there’s a low voltage, switch-ing regulator power supplyinside every computer that’son everyone’s desk in theworld. We’ll discuss thesetypes of power supplies infuture issues of Slot TechMagazine.

But not all power suppliesare switching regulatorpower supplies. Some powersupplies are of the muchsimpler “linear” or “conven-tional” power supply design.These supplies are used in avariety of applications as well.In some cases, we’ll even seea power supply that doesn’tactually power anything atall. What’s up with that?Read on and see.

First of all, what the heck isa power supply? Surely thepower for the game comesfrom the AC wall receptacle.Isn’t that the power supply?Well, not really. It is a powersource for sure but it is nota suitable power supply.

You see, the AC power thatcomes from the wall recep-tacle is really good for somethings but not others. Alter-nating current is great forthings like weed-wackersand toasters and hair driersand fluorescent lights and in-candescent lamps and such.But AC is not useful as apower supply for electronics.Electronic systems such asradios, televisions, comput-ers and VCRs require directcurrent to operate.

Regardless of the fact thatthese devices might beplugged into the 120 volt ACwall receptacle, once insidethe box the first thing thathappens to the AC power isthat it is turned into DC by

the unit’s power supply.That’s what a power supplydoes. The power supplytakes the 120 volt AC inputand turns it into a DC out-put. This DC is then used topower the electronics.

In addition to changing thepower from AC into DC, apower supply is likely tochange the voltage as well.For example, a computer re-quires +12 volts DC, +5 voltsDC and +3.3 volts DC. Thecomputer’s power supplytakes the 120 volt AC inputand provides these low volt-age, DC outputs. The powersupply in a plasma displaymight do just the opposite,taking 120 VAC in and pro-ducing a +200 volt or higherDC output. In some moni-tors, the main B+ power sup-ply has a +120 volt output.In this case, the 120 volt ACwasn’t changed in voltage atall.

Regardless of whether theoutput is lower, higher or the

Slot Tech Product SpotlightSlot Tech Electronics 101Understanding Linear

Power Supplies


same voltage as the input,the power supply alwayschanges the AC input into aDC output.

Alternating Current

Before we take a detailedlook at power supplies, let’stake a closer look at alternat-ing current. The best way tounderstand alternating cur-rent is to look at AC in theform of a graph as shown infigure 1. This is a simplegraph that shows TIME inthe horizontal direction andVOLTAGE in the vertical di-rection.

The horizontal line down themiddle of the graph repre-sents ground. Ground iszero volts. Any time the volt-age is positive, a line or pointis drawn above ground. Nega-tive voltages are representedby a point or line drawn be-low ground.

The alternating current weuse as a power sourcechanges polarity 120 timeseach second. As the ACmakes the change from posi-tive to negative and backagain, it doesn’t instantlychange polarity. It takes a bitof time for the voltage to risefrom zero volts, increasing involtage until it reaches itsmaximum or “peak” positivevoltage. The voltage does notremain at the peak, however.An instant after reaching itspeak, the voltage begins todrop. The voltage continuesto drop until it has returnedto zero volts.

But we’re not through yet.

After the voltage hasdropped to zero volts, it keepsdropping. It has become anegative voltage now. This iscalled the “zero crossing.”The voltage continues todrop until it reaches a nega-tive peak voltage that is justas far below zero volts as thepositive peak is above zerovolts. In other words, thepositive and negative peaksare the same voltage but op-posite polarity. After reach-ing its negative peak, the volt-age then rises back up tozero volts. This completes onecycle of alternating current.The process is then repeated60 times each second. Thefrequency of the AC power inNorth America is 60 cyclesper second or 60 Hertz. Else-where in the world, it is 50Hz.

This graph that we have justcreated is called a waveform.This particular waveform hasa name. It’s called a sinewave. No matter in the worldyou are, the AC power is al-ways a sine wave. You’ll prob-ably see a tiny sine wave onyour digital multimeter thatindicates the AC voltage set-ting.

So if the graph of AC poweris a sine wave, what does thegraph of the DC output of apower supply look like? Ofcourse, it’s just a straightline. DC does not changepolarity the way AC does. Itdoesn’t change voltage theway AC does either. Becausethe voltage and polarity re-main constant, the graph isjust a straight line.

So, somehow the power sup-ply changes the sine waveinto the straight line. Itchanges AC into DC. Let’ssee how it works:

Changing the Voltage

In a linear power supply, ifthe power supply is going tochange the output voltagesuch that it differs from theinput voltage, it will gener-ally do that first and use atransformer to do it. Welooked at transformers in theOctober, 2001 issue of SlotTech Magazine.

Let’s begin this month’s lookat linear power supplies witha 12 volt, step-down trans-former. The primary input ofthe transformer is connectedto the 120 volt AC input. Theoutput voltage at the second-ary winding is, of course, 12volts AC.

Let’s power something withthis transformer. Let’s say forthe sake of discussion thatwe want to power a 12 voltmotor. We connect the 12volt motor to the 12 volt sec-ondary winding of the trans-former, plug it in and . . .nothing happens. The motordoesn’t turn at all. What’sup?

This is quite puzzling for aminute or two until we real-ize our mistake. Upon closerinspection of the motor, werealize that this is a DC mo-tor and we’ve connected it tothe AC output of the trans-former. Remember that atransformer is strictly an ACdevice. It uses AC as an in-


put and gives us an AC out-put.

The way a DC motor worksis that the polarity of thepower supply determines thedirection of rotation. Ofcourse, this is how a revers-ible hopper works. The mo-tor is controlled by the po-larity of its power supply.

In this case our motor doesn’tturn because the output po-larity of the transformer isreversing so quickly that be-fore the motor even has achance to begin its rotationin one direction, its powersource has already been re-versed. In fact, a DC motorconnected to an AC powersource will just sit there andvibrate. It will not turn at all.

Rectification

Let’s see what we can do torectify this problem and getthe motor to turn. Let’s breakthe source path of this cir-cuit and connect a diode inseries with the transformer

and the motor as shown infigure 2. Remember that ina series circuit, all of the cur-rent must pass through onecomponent in order to get toanother component. In thiscase, the electric currentcoming from the transformermust pass through the diodebefore it gets to the motor.Let’s see how this works:

Since AC is constantlychanging polarity, let’s lookat things one step at a time.When point A is positive andpoint B is negative, current(flowing from positive tonegative) flows through thediode to the motor. This isthe source path. The currentthen flows through the mo-tor and follows a return pathback to the negative side ofthe transformer. This currentflow pushes the motor andstarts it rotating in one di-rection. Let’s call it clockwise.

1/120th of a second later, thetransformer’s polarity is re-versed. Point A is now nega-tive while point B is positive.

With the polarity reversed,the current now wants toflow from B to A but it can-not. The current wants toflow from point B to the mo-tor. That part is fine butwhen the current gets to thediode, it is reverse biased andwill not conduct in this di-rection. That’s just the sameas if the diode is completelyopen and, of course, no cur-rent actually flows at allwhen the polarity is re-versed.

At this point, instead of themotor receiving a reversedpulse, pushing it back fromwhence it came (rotationallyspeaking, that is) the motorsimply coasts along in thesame rotational direction asit was being pushed whenpoint A was positive andpoint B was negative.

1/120th of a second later, thetransformer’s polarity is re-versed once again and themotor receives another pulsethrough the diode and getsanother shove. The processis repeated 60 times eachsecond and the motor is nowturning.

By adding just a single di-ode, we have changed the ACinto DC. The process ofchanging AC into DC iscalled “rectification.” We hadto rectify the problem of ACby turning it into DC with adiode. Another term for di-ode is “rectifier.”

If we look at a graph of thecurrent flowing into the mo-tor, it now looks like thewaveform shown in figure 4.

During the positive half-cycles, current flows rightthrough the diode andstraight to the motor butwhen the polarity is re-versed, no current flows atall. During the negative half-cycle, the voltage is zero.

This type of DC is called “pul-sating DC” for an obvious rea-son. The current comes outin pulses. It’s nowhere nearthe straight line of pure DCthat we’re looking for but atleast we can make the motorturn. This type of power sup-ply (using just a single diode)is called a “half-wave” powersupply because it uses justhalf of the AC sine wave.

What do you suppose hap-pens if the diode is reversed,with the cathode connectedto the transformer’s second-

ary winding and the anodeconnected to the motor asshown in figure 3? This willreverse the polarity of thecurrent flowing to the motorand the direction of themotor’s rotation will reverseas well. Let’s see how thisworks:

When point A is positive andpoint B is negative, no cur-rent flows because the diodeis reverse biased. But whenpoint B becomes positive andpoint A is negative, currentflows from the transformer,through the motor, throughthe diode (now forward bi-ased so that it will conduct)

and back to the transformer.A graph of the current flow-ing into the motor now lookslike figure 5. It’s still pulsat-ing DC. This time, it’s nega-tive.

By turning the diode around,we have created a negativepower supply. In fact, that ishow we create a negativepower supply. We simply re-verse the diode. This is, infact, an important thing toknow about power supplies.When the output of a powersupply comes from the cath-ode of a diode, it is a positivepower supply. When the out-put comes from the anode ofa diode, it is a negative powersupply.

Full-Wave Supply

The half-wave power supplyallows us to power the motorand make it turn but it’s notvery efficient. We have powerto the motor for only half ofeach cycle. During the otherhalf cycle, the voltage andcurrent is zero. The current



exists. It’s just going thewrong direction. If we can useboth halves of the AC, we’llbe twice as efficient. This iswhere the bridge rectifiercomes in.

The bridge rectifier is simplyfour diodes connected in acircuit as shown in figure 6.A bridge rectifier can be asingle unit or it may be com-prised of four individual di-odes. Starting when point Ais positive (see figure 7) cur-rent flows through D1, themotor, and D3 before return-ing to Point B. When the po-larity reverses and point Bbecomes positive, currentflows through D2, the motorand D4 before returning topoint A.

Take a closer look at diodeD2. Can you see what it’sdoing? Instead of just cuttingoff the current flow when it’sgoing the wrong direction,D2 acts like a detour and re-directs the current to whereit’s needed, at the positiveoutput of the bridge rectifier.Notice too that the positiveoutput of the bridge rectifieris found where the two cath-odes come together. Remem-ber, when we take the out-put from the cathode, it ispositive.

A power supply like this iscalled a “full-wave, bridge-rectifier” power supply. Agraph of the motor currentwould now look like figure 8.Notice that it’s still pulsatingDC but now there are twiceas many pulses in the sameperiod of time making it twiceas efficient.

A full-wave, bridge-rectifier

power supply can be positiveor negative. Typically, thenegative side of the bridgerectifier is grounded and theoutput is taken from thepositive side. This of course,is a positive power supply. Al-ternatively the positive sideof the bridge rectifier can begrounded and the outputtaken from the negative.

Another way to obtain a full-wave power supply is to usea center-tapped transformerand just two diodes as shown

in figure 9. When point A ispositive, current flowsthrough D1 and the motor.The return path is throughthe grounded center-tap ofthe transformer. When pointB is positive, current flowsthrough D2. Notice how,once again, D2 acts like adetour and redirects the cur-rent up to the top of the mo-tor. As before, the returnpath is through thegrounded center-tap of thetransformer.

The output of this power sup-ply is full-wave, pulsating DCjust like the bridge rectifier.However, because this de-sign utilizes just one half ofthe transformer secondary ata time, the output voltage iscut in half. In other words,in order to obtain a 12 voltoutput, a 24 volt, center-tapped transformer must beused.


This is called a full-wave, cen-ter-tapped power supply. Re-versing the two diodes cre-ates a negative power supply.With their anodes tied to-gether, we create a negativeoutput.

Here’s another neat trick. Wecan create a power supplythat’s both positive and nega-tive at the same time by us-ing a center-tapped trans-former and a bridge rectifieras shown in figure 10. It’scalled a split supply. We ob-tain a positive output wherethe two cathodes of D1 andD2 are tied together and anegative output from thejunction of the two anodes ofD3 and D4.

Filtering

Now we’ve succeeded in con-verting the AC into DC us-ing one of the methods de-

scribed above (There are afew other methods, by theway. However, they are rarelyused and you’re not likely tosee them.). Unfortunately,we still cannot use this powersupply to power any elec-

tronic system. Referringagain to the graph in figure8, the full-wave, pulsating DCwe have created is still noth-ing like the straight line weneed. The voltage drops tozero volts twice each cycle,during each zero crossing ofthe sine wave.

This problem is solved byadding an electrolytic capaci-tor to the power supply (seefigure 11) following thediode(s). Let’s see how add-ing the capacitor changesthe output of the power sup-ply:

When the output of the di-

odes is at its peak voltage,electric current flows not onlyinto the load but into the ca-pacitor as well, charging thecapacitor to the peak voltage.After reaching its peak volt-age, the output from diodeswill drop. However, the ca-pacitor is now fully chargedand it keeps the voltage (andcurrent) up until the nextpulse comes along (just 1/120th of a second later) andrecharges it. In other words,the capacitor first acts as aload, taking in a charge fromthe diodes, then as a source,releasing its stored energyinto the actual power supplyload itself.

A graph of the output cur-rent now looks like a straightline. This is now known as“filtered DC” as the electro-lytic capacitor has filteredout the peaks and valleys ofthe pulsating DC. In fact,this capacitor is called the“filter capacitor.”

The analogy here is your car.While you are drivingaround, the vehicle’s genera-tor or alternator powers theelectrical system of your car.This is analogous to the timewhen the output of thediode(s) is at the peak. Dur-ing this time, your car bat-tery, like the filter capacitorin the power supply, is be-ing charged as well.

When you stop the engine,the output of the generatordrops to zero. However, youcan still listen to the radioand run your headlights andall of the other electrical sys-tems in the car because the


battery is fully charged andremains so until you start theengine again. In the sameway, the filter capacitormaintains its charge andpowers the load betweenpulses. Instead of droppingto zero volts between pulses,the filter capacitor maintainsthe voltage more or less atthe peak output voltage ofthe diode(s).

Peak Voltage

Which brings us to anotherinteresting phenomenon inthe world of power supplies.Earlier in this discussion, weused a 12 volt transformer topower a motor. If we were tomake a full-wave, bridge rec-tifier power supply using thistransformer, and hang a fil-ter capacitor on the output,the output voltage would bearound 17 volts DC, not 12volts DC as you would imag-ine. Huh? Where did the ex-tra voltage come from? Well,in fact, it was always thereand it came from the trans-former. Try to follow me onthis. It has to do with the waywe measure voltage.

DC is easy to measure. Re-member, it’s just a straightline as seen on a graph. Nomatter when you measure it,it’s always the same voltage;it’s always the same polarity.But how the heck do youmeasure something like ACwhen it’s always changing?It starts at zero volts, climbsto a positive peak, drops backto zero, drops to a negativepeak and returns to zerovolts, all in the space of 1/60th of a second.

As it happens, there are ac-tually a few different ways tomeasure AC. One is to mea-sure the voltage between thepositive peak and the nega-tive peak. This is known as a“peak-to-peak” measure-ment. Peak-to-peak voltagemeasurements are generallyreserved for non-symmetri-cal, non-repetitive waveformssuch as audio or video sig-nals. Since a sine wave is arepetitive, symmetrical wave-form, the positive peak is ex-actly the same voltage as thenegative peak. In this case,measuring the voltage be-tween ground and eitherpeak reveals what is known

as the “peak” voltage of theAC. In the case of a sine wave,the peak voltage is alwaysexactly half of the peak-to-peak voltage.

But this is still not a whollydescriptive measurement be-cause the voltage is reallynot at its peak for very long.In fact, the peak voltage isreally just an instant in time.Throughout the remainder ofthe cycle, the voltage is be-low the peak. There is a thirdmeasurement for alternatingcurrent that is an averagemeasurement; a measure-ment that takes into accountthe peak voltage as well asall of the other voltages atevery point along the curveof the sine wave. It’s knownas the RMS average.

RMS stands for “root meansquare.” RMS is a math-ematical average that takesthe value of every point alonga curve, squares them, addsthem together, takes a meanaverage by dividing the sumof the squares by the num-ber of points and finallytakes the square root of themean average. Whew! Now


you know why I flunked outof engineering and I remain,to this day, a high schoolgraduate.

The RMS calculation differsfor each type of waveform butsince our AC power is alwaysa sine wave, we only have tomake this calculation once.In fact, we really don’t haveto make it at all becausesomeone else has alreadydone it for us a hundredyears ago. It turns out to be.707 X PEAK. The RMS aver-age of a sine wave is 70.7%of the peak voltage.

In a nutshell, the RMS aver-age is a measurement of theAC’s ability to perform work.Look at it this way: Supposewe connect a light bulb or atoaster to an AC source of ex-actly 100 volts peak. Thebulb glows with a specificbrightness and gives off acertain amount of heat. Thetoaster toasts a slice of deli-cious (and nutritious) whitebread in exactly 100 sec-onds.

Connect that same light bulbto a DC source, and it willrequire only 70.7 volts DC tolight the bulb to the exactsame brightness. ConnectDC to the toaster and thetoast will be done to thesame degree of “toastness” injust 70.7 seconds instead of100 seconds.

If you think about it for a sec-ond, you’ll realize why thisis. Although the AC peaks at100 volts, it’s not at 100 voltsall the time. Therefore, ittakes less DC (which is con-

stant) to perform the sameamount of work as the peakvoltage of an AC source. Av-eraging the peaks with thetimes that the voltage is lessthan peak (including the twozero-crossings, rememberthose?) reveals the magicnumber: the RMS average ofa sine-wave is .707 times thepeak voltage. In other words,70.7 volts DC performs thesame amount of work as 100volts peak AC.

So what does all this have todo with the reason why theDC output of a filtered powersupply is apparently higherthan the AC voltage comingout of the transformer? Okay,here’s the deal: Transform-ers are rated by their RMSvoltage. In fact, just about allmeasurements of AC powerare RMS unless stated oth-erwise. Remember that 12volt transformer? Well, that’sactually the RMS output volt-age. (In fact, it’s very likelyto be a 12.6 volt RMS trans-

former rather than an exact12 volts.) The output of thetransformer actually peaks ataround 17 – 18 volts (RMS X1.414 = peak).

When the alternating cur-rent is rectified by the diodesand filtered by the filter ca-pacitor, the capacitor keepsthe voltage at the peak! Thatis why we seemingly obtaina higher DC output voltagethan the AC voltage we usedas an input. Although wecalled this a 12 volt trans-former, that was an RMS rat-ing. The output of the trans-former actually peaked at 17-18 volts and that’s what weget out as DC. This is totallynormal. It happens everytime. When, for example, werectify and filter the 120 voltAC current from the wall re-ceptacle, the DC outputends up at around 170 voltsDC.

Next Month: Voltage Regu-lation

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