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Yak! I think I fried my PC.... turns on and off in a loop...

L

lcymet

Junior Member
My computer was recently working fine, and I noticed the cpus were running hot, so I unplugged it and openened the case to give it a cleaning. When I put everything back together and plugged it in - it turned itself on when I switched the power supply on, without pressing on the power button. It posted, did the memory test fine, then turned itself off after the bios ran through.... then, a moment later it turned it self on again. I shut the power supply off, unplugged it, made sure to ground myself and opened it up again - thinking maybe I loosened the memory, and then when I pressed on the memory - it powered up again! (Just for a second). Fixing the memory didn't help.

Any thoughts? Could I have shorted the motherboard? Should I be worried about any damage to the other components in the PC?

Thanks,

Laurence

My Machine:
Full Tower case
520 watt Vantec dual stealth power supply
Dual AMD Athlon MP 1600+ (see note below) w/ bundled fans
Tyan Tiger MP rev 1.03 S2460
1 gig ECC registered ram
80 gig maxtor IDE, 120 gig WD 8 mg cache IDE
MSI FX5600 Nvidia card 128 DDR
SB Audigy
3COM 10/100 card

*note: This motherboard had been recently fixed by Tyan to correct a manufacturers defect where the motherboard power connector was drawing from the 5v rail instead of the 12v.
 
You could have shorted something, that sounds like the most likely culprit. Start by unplugging the power cord and resetting the cmos. At the same time, make sure everything is tight and reseat the power connections. I would remove any extra PCI cards, extra ram, or usb devices. Turn it on and let it sit in bios...if it restarts there, you know you have a real problem. If the computer does not restart or shut down in the bios, the hardware might still be o.k. Boot it up and see what happens.
 
If the problem persists, try this:
  • Turn off the PSU's power switch on the rear
  • Disconnect your case's power-switch wire from the motherboard
  • Turn the PSU's power switch on again.
If the computer remains off, where it would have started before, then your case's power switch is probably mechanically stuck in the "pressed" position, even if it doesn't look like it from the outside. This would explain why the system powers on when you give the PSU power (it sees the button "pressed" and powers up) and also why it powers itself down again (it sees the button continuing to be pressed, or so it thinks, and that is a signal for a motherboard to power down again).

If this is indeed the problem, fidget with the case's power switch to see if you can un-stick it. Removing the case's bezel may help, since the button on the bezel is usually just an actuator for the actual switch itself. Good luck, hope that helps 🙂
 
Hmm... the power button sounds like a possibilty - the machine will now load up windows 2000, and once everything is running, windows will shut itself down. (as if I pressed the power button!!!)... also, I'll cry if I shorted my machine out. 😉 I am currently not near my PC, but I will try these suggestions promptly.

Thank you kindly for your suggestions. They are highly appreciated.
 
So I tried disconnecting the power switch and it still failed, same for the reset switch.

I disconnected and removed everything possible. and it is still turning on without pressing the power button, loading into win2k, and promptly re-boot (as if the power is switched off an on). And sometimes it won't even make it into windows. The wierdest thing is - with the power supply switched off, if I move the box, or touch something inside the box - the machine will power up for a second and then turn off. And at one point it re-booted (or the power reset) while sitting the bios.

I'm assuming at this point my motherboard is fried (the Tyan tiger MP has given me probs from the start), but could it be the power supply?

Thanks for any input.
 
If the PSU switch is set to off, the system should simply never power up. None of the rails should have any power at all.

It might be a grounding issue going on. It might be a combination of wake-on-LAN combined with CPU overheating or CPU fans not connected. First thing I would do is probably check to make sure the motherboard and PSU aren't grounding out onto the case, and then I'd replace the PSU (or swap in a known good one).
 
I've had similar symptoms to yours when capacitors on the motherboard had gone bad. Check for that. (at least one will likely have swollen or be leaking around the top)

My first reaction was the power button being stuck...but if the switch is disconnected and it still does it...that is very odd.

It also might be a heat issue, are you sure the CPU fans and heatsinks are all ok? Did you reseat them during your cleaning? You're sure you didn't possibly chip a cpu core, forget to apply thermal past, anything like that?
 
Hmm.. I'll check for a bad capacitor - and yes it's quite possible I screwed up a cpu in my meddling around. I'll redo them properly (new paste and all) and have a look.

I'll also try a different powersupply - seems highly suspect that the machine is powered even though the switch on the supply is off. Unless the MB can carry enough charge to power up for a second.

The CPU fans are going fine and the cpu's are cool.

Thanks everyone for your help.
 
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