No Power to the PC

A neighbor's PC does not power up when I turn on both the switch in front and in the back. Is it possible this could be a bad power cord? I attached the cord to an unused PC PSU and turned it on. The fan doesn't move. Is this normal? Maybe it requires a load to start the fan in action?

Broken switch on the PC? It seems odd this was working when I left his house. The only thing I didn't bring of his was the power cord. Clues? Tests?

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                          Wayne Watson (Nevada City, CA)

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W. Watson
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This is often the case, but not always.

First make sure there's power going into the cord :-) Outlet live? Power strip turned on? Seated firmly on both ends? etc. If so...

Turn off the switch on the back of the PS. Unplug all the output leads of the PS. On the 20 (or 24) pin connector that provides main power to the motherboard, install a jumper (a paper clip works) between the green wire and any black wire. Turn the switch on the back of the PS on. The power supply should run. If it doesn't, the power supply is bad. There's a fuse inside, but it's the nature of switchers that whatever blew that fuse will probably blow the replacement fuse immediately. So don't bother; just replace the PS.

If the PS _does_ turn on with the jumper installed, then it could be the front panel pushbutton, or its wiring. It could also be processor, RAM, and/or motherboard.

Note where the front panel switch connects to the motherboard. On some PCs (ex: Dell), this may involve a continuity check but in most cases you can follow the wires by eye to a motherboard connector.

Plug the 20 (or 24) pin connector in, and also the 4-pin black/yellow connector (near the processor), if there is one. Using a small screwdriver, momentarily short the two motherboard pins you just identified as the power on pins. If the system powers up, turn it off, plug the rest of the power supply outputs back in, and try again. If it still works, replace the front panel switch and associated wiring.

If it powers up with just the motherboard power connector(s) attached but not with all the power plugs attached, then some peripheral is shorted. Unplug power leads one at a time until you find it.

If the power supply fires up with the jumper but not any other way, then it's beyond the power of usenet to help you.

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Gordon S. Hlavenka           http://www.crashelectronics.com
               It's bad luck to be superstitious
Reply to
Gordon S. Hlavenka

I once got stumped on a friends PC. Same symptoms. First thing I did was pull the PSU and test it. It worked perfectly fine on the bench,powered up,all voltages were right-on (actually much closer to spec. than most PC supplies I've seen!) Voltages all held up well under load,etc,etc. Hmm,Must be the Motherboard. Double check the PSU on the bench. (A-ok!) Order a new Motherboard,No change! (oh no!) Triple,quad,and quintuple check PSU. Finally get so frustrated that I give in,buy a PSU 'for the heck of it' I'll be damned if it didn't fire right up.

Upon close inspection of the old PSU,The output filter caps had dried up (one had bulged a bit) and apparently there was just a bit too much ripple for the mo-bo's liking,and it refused to boot. It didn't look tooo terrible on the scope,but it was kinda nasty.(typical cheap SMPS crud.) Other than that the PSU *appeared* to work perfectly.

Friend got a new mo-bo (yay! no leaky mo-bo caps for a few more years),faster CPU,and a bigger PSU out of the deal.

I got a lesson in PSU testing.. Bust out the scope and scrutinize that sucker. The DMM and dummyload(s) don't always cut it.

If you don't have a scope,do a visual inspection: -carefully- pop the cover on the PSU (may void warranties,etc!) and have a look at the caps near the output wires. If they're bulged,leaking goo,etc. replace the supply.

My darn server needs a new power button...Sometimes I have to push it a few times for it to work.I expect it may completely fail sometime soon.

Look at my reply above,That's exactly what happened to me. Worked perfectly with the jumper on the bench,Nada Damn Thing on a Motherboard.

Reply to
PhattyMo

That's a new one on me; I'd have been chasing it for a while too. But noted for future reference :-)

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Gordon S. Hlavenka           http://www.crashelectronics.com
               It's bad luck to be superstitious
Reply to
Gordon S. Hlavenka

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