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New build - odd power problems

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February 12, 2010 2:47:05 AM

Hi.

Yesterday I put together a new computer to replace one that was damaged in transit. The new one uses the hard disk and video card of the old one, but all the other parts are new (including the case).

The system booted fine when I first switched it on, and I was able to use it for about half an hour before it abruptly switched off. When I then pressed the power button the system started up for about a second and then shut off again.

Now, this morning, I decided to try again. When I turned it on, the system booted fine! I was again able to use it for about 20-30 mins, this time installing the drivers from the motherboard CD, and then the computer shut off again.

The computer consists of:
CPU: Intel i5 750
Motherboard: Gigabyte GA-P55-UD3
PSU: Corsair VX-550
RAM: Corsair XMS 3 4Gb
Case: Antec VSK-2000 (I mention this because it includes a fan)
Video card: XFX ATI Radeon 4870 (Salvaged from old computer)

Now, three details come to mind. First: I got someone in to examine my old computer, and to cut a long story short he concluded that the video card was busted because on replacing it (and other busted parts) temporarily, the old computer was able to display stuff on the screen when before it couldn't. However, when in my new machine the video card has worked fine.

The second thing is: the screws I used to secure the motherboard came from the case - none were packaged with the motherboard. The manual did not mention using washers to separate the screws from the motherboard, and a brief google gave me the impression that this kind of motherboard actually uses the screws to ground itself.

Finally, the motherboard wasn't totally, completely flush against the supports. Some of the motherboard holes were sticking up and others were exactly resting on the holes. I screwed them all down. I've since been wondering if this slight bending of the board would cause these problems...

Any ideas? I would have thought it would be the PSU, but I was specifically recommended to get a Corsair one because they're supposed to be reliable...
February 12, 2010 3:06:49 AM

Our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...

To eliminate case problems, breadboard the system:
http://www.tomshardware.com/forum/262730-31-breadboardi...

If your case or motherboard didn't come with a system speaker (Antec cases don't seem to) you can buy one here:
http://www.cwc-group.com/casp.html
You will need it for troubleshooting.

Corsairs are good PSU's. (I own three.) But even they can be DOA. Try to borrow a known good PSU of similar capacity. Or better yet, see if you can test your PSU in another working system. If you cannot do that, use a DMM to measure the voltages.

Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot. All voltage readings must be +/- 5%.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

This checks the PSU under no load conditions, so it is not completely reliable. But if
it can not pass this, it is dead.

If this passes, reconnect the PSU and repeat. You can measure the voltages from the back of the main power connector.
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February 12, 2010 3:59:30 AM

The PSU is not dead! Twice, the system has booted and run for 20-30 minutes! I was wondering if there might be something wrong with it causing it to conk out after a certain period of time.

I don't have spare parts for testing. I'm interested to hear what people think the issue might be, if they have any experience with the particular components or this particular issue is familiar. It's not as straightforward a problem aas "the computer doesn't work".
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February 12, 2010 10:35:50 AM

Oops. Didn't read closely enough.

All motherboards depend on the screws to ground the case.

Try breadboarding the system.
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!