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Bad power supply?


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Recently my PC which had been running for about 5 hours suddenly shut down. I rebooted and it ran OK for a few hours and did the same again. After a dozen more reboots all it does when the front power button is pressed is power-up for 1 second max then shut down. The light at the front comes on (and stays on after shut down!) and the chip and case fans run for that second. If I try to reboot nothing happens unless I switch the power supply switch from on to off and back again. Then it reboots for a second again when I press the power button.

I haven't made any hardware or driver changes recently so was wondering if anyone had any suggestions. Could the power supply be faulty or something tripping it out?

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How do I clear the CMOS?

 

You need to open up the case, go locate the Battery on the motherboard, remove it, then Change the Jumper from 1-2 to 2-3

 

Check your motherboard manual for help on locating it.

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I did a bit more investigation. If I unclip the 4 pin ATX 12V connector from the mobo, but leave the 20 pin connector attached to the mobo then he computer will power up (power to mobo fan, case fan drives etc), but not boot up. Any more thoughts? Points to mobo or power supply?

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most likely it will be the psu. is this system homebrew or is it from a manufacturer?

 

The system is a bit of both. I bought it a year or so ago from a small independent guy who sells through ebay. This is the first problem I've encountered. The only thing that may have caused the problem is that a year ago I added an extra hard drive, DVDdrive, sound card and TV card which may have put too much strain on the 400W psu.
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Unless its a very very good brand its unlikely the psu actually outputs 400w. Manufacturers tend to grossly overstate this figure.

You can get a psu tester for a few dollars but I dont think they tell you the all important rails voltages.

However from the sounds of it, it does seem as though the mainboard is the culprit.

Edited by Andrew S.
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Now that you say you got it from ebay, you got a bad PSU from what I know. Most sellers will give you a PSU bundled with the case, it sucks and lasts less then a year for sure. Try looking at that one first.

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  • 2 weeks later...

Just to tie up the thread and maybe help those out with similar problems. It was indeed a PSU fault. Stuck a new one in and worked fine. The old one was light as a feather...no wonder it didn't last long.

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