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Tutorial: Suspect a Dead PSU? How to be sure

By kirock
Aug 2, 2006
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  1. So you turn on the computer and nothing happens, it could be a broken case switch and therefore the PSU never gets the signal to turn on. Or it could be a dead PSU or something else dead pulling down the output of the PSU.
    Here's what you do:
    1) Unplug the leads to the case switch at the mobo and jumper them with a small piece of wire. Now turn on the main power switch at the back of the PSU. If nothing happens, we're a long way to proving the PSU is dead.
    2) If above procedure caused nothing to happen, now we get a little more into it. Remove the 20pin PSU connector and the 4pin CPU connector to the mobo, all other psu connections can stay put. Using a small wire (a paper clip will do) jumper pins 14(the only green wire) and any BLACK wire (let's say pin 13 or 15) on the 20 pin PSU connector. Now turn on the main PSU switch. Your PSU should come to life (HDD spins up, and fans spin).
    Below is a pic of the 20 pin connector
    [​IMG]
    From the pic you can see that pins 13 and 15 are ground pins, that's why you can use either one. You want to ground pin 14. This is all the case switch does via mobo traces out to the case switch leads. Well it does go thru a FET or Bipolar transistor to make the actual connection, this is how Windows can soft shut down the PC.
    3) If nothing still happens then start removing 4 pin molexs one at a time, starting with the video card (if it has one). This will eliminate any peripherals "holding" or "pulling" down the PSU. After all connections are removed and still nothing, then your PSU is dead for sure.
    4) Edit: I forgot this possibility. If after step 2, all fans spin up and HDD spins, but at step 1 nothing works, then it's most likely a faulty mobo. And most likely that little FET or Bipolar transistor or at least the circuit that turns that on. Either way at this point you're best to take it in for service or RMA your mobo back if applicable.
    Hope this helps, Cheers.
  2. Tedster

    Tedster Techspot old timer..... Posts: 10,074   +13

    Antec sells a power supply tester for $12 available at circuit city. It has 5 LEDs to tell you if you're getting good power on all rails plus it has voltmeter ports in the back to plug in a voltmeter.

    Good investment and beats swapping out a PSU (time and money) if yours is still good.
  3. rav4guy

    rav4guy TS Rookie

    guid

    hi there,
    after i put jumper between 14 and ground my HDD kicked in but when i removed jumper my computer still didnt work,my question is if your HDD works when you put jumper what does that mean and what is next step

    thanx
  4. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    Hello and w elcome to Techspot.

    It means you need to try another psu. If that doesn`t help, there`s a very good chance your mobo is faulty.

    Regards Howard :wave: :wave:
  5. rav4guy

    rav4guy TS Rookie

    Aopen ax6b

    when i try to boot my computer you can hear fan running and my dvd ram light flashes and red light on case stays on and no green light which usualy comes on normaly start up,my mobo is Aopen ax6b .any ideas what cause that .prior to that i swapped psu with another psu then when i put psu back on this problem showed up..thanx
  6. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    As I said earlier, if another psu doesn`t solve your problem, your mobo is probably faulty and will need to be replaced.

    Regards Howard :)
  7. Ph30nIX

    Ph30nIX TS Rookie Posts: 359

    Good tutorial, I used the same technique on my friends pc after he got his mobo replaced, at the time it was top of the line mobo. Turns out PSU was just bugered so it ended up sending whole pc back to the shop and got fixed.

    Maybe someone should include some pictures, or even a video of this just to make it more clear.
  8. k.jacko

    k.jacko TS Rookie Posts: 743

    I'm a little confused about point 1) in the tutorial. Can anyone translate it better for me please.
    Does it mean the 2-pin power switch lead that is attached to the case?

    The other points I understand.
  9. kirock

    kirock TS Rookie Topic Starter Posts: 1,598

    Yes you are correct. unplug the case switch leads to the mobo. On the mobo where those wires just came off, use a piece of wire to jumper those 2 pins. This is eliminatiing the Case Switch, or faulty leads to it, as the problem. When you turn on master power switch at back of PSU and nothing happens, then you need to continue to step2. If all is fine then it's either a bad case switch or bad leads going to from mobo.

    Cheers.
  10. pc-essentials

    pc-essentials TS Rookie

  11. Oversoulx2

    Oversoulx2 TS Rookie

    So i tested my PSU to see if was dead. The test was awesome and learned that there was nothing wrong with the PSU. So I'm assuming what's wrong with my PC is either the CPU? or the mobo. How can you be sure the mobo is faulty? When everything is connected, a green light on the mobo is on.
     
  12. howard_hopkinso

    howard_hopkinso TS Rookie Posts: 25,948   +19

    You can have the cpu tested at your local pc repair shop. This should only cost a few dollars.

    If that checks out ok, then it has to be the mobo that`s dead. the fact that there`s a green light on the mobo, is no indication that the mobo is ok.

    Regards Howard :)
  13. kirock

    kirock TS Rookie Topic Starter Posts: 1,598

    Howard is correct, but I just want to be clear.
    Step 1: removed case switch leads......: what happened?
    Step 2: removed 20pin connector........: what happened?

    If the PSU doesn't come on after Step1, but does come on at Step2, there's a really good chance the mobo is screwed. But there's noway of telling if the CPU is dead (it's part of mobo) or other parts of mobo. So best thing now it take CPU to some where and have it power up a PC. All you need is a friend with the same socket type mobo (but be careful, if your CPU is really dead you might damage his mobo/PSU).

    Cheers.
  14. Appzalien

    Appzalien TS Rookie Posts: 96

    Great, I love the colored diagrams, you can put a jump wire between the green PS power and a ground to make a powersupply run while its ouside of the PC on versions without a switch as well.
  15. EyesofNova

    EyesofNova TS Rookie

    There are much easier ways of telling if your psu is dead that don't require potentially electrocuting yourself if you have no idea what you're doing. First, most motherboards have LED light indicators to show if they're getting power that will turn on even if the motherboard is fried. 2nd thing to check is when you push the power button if the fans still start to spin on the case and the heatsink. This mean you're getting power but your motherboard/cpu maybe fried. Most motherboards will give you indicator beeps if your memory, cpu, or video are dead so look them up and determine which it is. If you suspect the power button is dead, a flat head screwdriver over the 2 pins will turn the computer on. Buy a new toggle switch from radioshack and go ghetto for a bit or move your reset switch over to the power switch pins. If that doesn't work then remove the power cord from the back of the psu, push the power button on the computer, this will discharge the remaining charge in the psu. Plug back into the wall and try turning the comp on. Finally this will help you determine if its the psu or the computer. BTW, PSU testers are not always accurate. I have 2 psu tester too and it has given me false positives before. All these are steps I've tried in real world situations on real peoples computers and I've have 100% success rate in determining customers problems.


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