The document provides instructions for testing a computer power supply using a multimeter to check voltage outputs. It describes disconnecting all internal devices, shorting pins 15 and 16 on the 24-pin motherboard connector, turning on the power supply, and using a multimeter to test the voltage levels on the 3.3V, 5V, 12V lines. If any voltages are outside the approved tolerance ranges, the power supply should be replaced.

1. The procedure of testinga powersupply
**USE CAUTION HERE (Thoughyou’donlybe shockedwithamax of 24 volts)
1. Plugthe powersupplyintothe wall.
2. Findthe big24-ish pinconnectorthat connectsto the motherboard.
3. Connectthe GREEN wire withthe adjacentBLACKwire.
4. The powersupply’sfanshouldstartup.If itdoesn’tthenit’sdead.
5. If the fanstarts up,thenit couldbe the motherboardthat’sdead.Youcan use a multimeterto
checkif there ispoweroutputfromthe powersupply.
Testinga powersupply usingamultimeter:
1. ReadImportantPC RepairSafetyTipsbecause of the dangersinvolvedwiththe process.
Manuallytestingapowersupplyinvolvesworkingcloselywithhighvoltage electricity.
2. Openyourcomputer'scase.In short,thisinvolves turningoff the computer,removingthe
powercable,andunplugginganythingelse connectedtothe outside of yourcomputer.Tomake
testingyourpowersupplyeasier,youshouldalsomove yourdisconnectedandopencomputer
case somewhereeasytoworklike ona table or otherflat,non-staticsurface.
3. Unplugthe powerconnectorsfromeach andeveryinternal device.
4. Group all of the powercablesandconnectorstogetherforeasytesting.Asyou're organizingthe
powercables,we highlyrecommendreroutingthem andpullingthemasfaraway fromthe
computercase as possible.Thiswillmake itaseasyas possible totestthe powersupply
connections.
5. Short outpins15 and 16 on the 24-pin motherboardpowerconnectorwithasmall piece of
wire.You'll probablyneed totake alookat the ATX 24-pin12V PowerSupplyPinouttable to
determine the locationsof these twopins.
6. Confirmthatthe powersupplyvoltage switchlocatedonthe powersupplyisproperlysetfor
your country.
7. Plugthe PSU intoa live outletandflip the switchonthe backof the powersupply.Assuming
that the powersupplyisat leastminimallyfunctional andthatyou've properlyshortedthe pins
inStep5, youshouldhearthe fan begintorun.Some powersuppliesdon'thave aswitchonthe
back of the unit.If the PSU you're testingdoesn't,the fanshouldbegintorunimmediatelyafter
pluggingthe unitintothe wall.
8. Turn on yourmultimeterandturnthe dial to the VDC(VoltsDC) setting.
9. Testthe 24-pinmotherboardpowerconnector:Connectthe negative probe onthe multimeter
(black) toany groundwiredpinandconnectthe positive probe (red) tothe firstpowerline you
wantto test.The 24-pinmainpowerconnectorhas +3.3 VDC,+5 VDC, -5 VDC(optional),+12
VDC,and -12 VDClinesacrossmultiple pins.
10. Documentthe numberthatthe multimetershowsforeachvoltage testedandconfirmthatthe
reportedvoltage iswithinapprovedtolerance.Youcanreference powersupplyvoltage
tolerancesfora listof properrangesfor eachvoltage.Are anyvoltagesoutside the approved
tolerance?If yes,replace the powersupply.If all voltagesare withintolerance,yourpower
supplyisn'tdefective.
11. Turn off the switchon the back of the powersupplyandunplugitfromthe wall.

2. 12. Reconnectall of your internal devicestopower.Also,don'tforgettoremove the shortyou
createdinStep5 before pluggingbackinthe 24-pinmotherboardpowerconnector.
13. Pluginyour powersupply,flipthe switchonthe backif youhave one,and thenturnon your
computeras younormally dowiththe powerswitchonthe front of the PC.
14. RepeatStep9 and Step10, testinganddocumentingthe voltagesforotherpowerconnectors
like the 4-pinperipheralpowerconnector,the 15-pinSATA powerconnector,andthe 4-pin
floppypowerconnector.
15. Once your testingiscomplete,turnoff andunplugthe PCandthenput the coverback on the
case.Assumingyourpowersupplytestedgoodoryou've replacedyourpowersupplywithanew
one,youcan now turnyour computerback onand/or continue troubleshootingthe problem
you're having.