What would cause a PC to shut down while still supplying power to certain components?

This is an HP Pavilion 533w running Windows XP. According to the owner, it's been working fine since 2002 (yeah, it's pretty old, but I'd like to fix it if I can). Then, just recently, it started shutting off a few minutes after being turned on. I opened it up and noticed that when it shuts off, only some components stop working. For example, the power supply fan continues to spin, but the case fan and the processor heatsink fan stops. The power LED on the front turns off, but the hard drive indicator lights up continuously. In addition, the hard drive continues spinning. If I hold the power button down, everything will power off completely.

I suspected it might be overheating, so I let it idle for a while at the BIOS screen, but the temperature stayed steady at 38°C. Then I popped in the Ultimate Boot CD and ran some stress tests, but it worked fine. Then, I thought it might be a problem with the power supply itself; maybe it would stop supplying power to some of the cables, so I tried a power supply that I know works, but that didn't help.

When Windows boots, it wants to run chkdsk, which I allow it to do. It finds a few problems, corrects them, and then the system powers off at around the end of step 2 or the middle of step 3. If I skip chkdsk, I can get to the desktop, but then the system shuts off between 3 and 5 minutes later. This made me think it might be a problem with the hard disk, so I ran MHDD32, but it reported no problems. I then booted a Windows XP Recovery CD and ran chkdsk from it, but it finished without problems.

At this point, I'm back to thinking it's a heat issue, but I'm not sure where to go from here. Does anyone have any suggestions?

David Brown

Posted 2010-10-14T19:38:24.037

Reputation: 1 373

Answers

Turns out 10 of the 1500μF capacitors on the motherboard were bad. Should be easy to replace.

David Brown

Posted 2010-10-14T19:38:24.037

Reputation: 1 373

Would like to hear stories of success re capacitors. I have an ailing mobo that I might want to try the same trick with. – Rolnik – 2010-11-08T04:41:28.623

It worked fine. I ordered replacements from BadCaps.net. It took me about 2 days to practice on an old motherboard I had lying around, because it was my first time soldering electronic components. But once I got the hang of it, the whole process only took 30 minutes or so. You'll need a soldering station (preferably with adjustable temperature, because in my case, the old solder melted at 450 degrees, while the new solder melted at 375), solder sucker, 0.22" rosin-core solder, and isopropyl alcohol to clean the contacts. – David Brown – 2010-11-08T15:29:59.180

75% chance you have a broken or underpowered power supply. Have you added any new hardware lately? Shoot, it could be you added something 2 years ago that put the PC 'on the edge'. Anyway, any departure from the 'stock' configuration could call on the PSU for more power -- which it can't deliver.

Rolnik

Posted 2010-10-14T19:38:24.037

Reputation: 1 457

According to the owner and what I've checked on HP's website, everything is original. The current power supply is 200W, while the one I put in as a test was 400W. But the symptoms didn't change. – David Brown – 2010-10-14T20:06:38.093

OK,probably not heat & probably not a bad PSU. My next guess is a short circuit somewhere. Is it possible that either a screw has come loose, or some metal filing has been liberated from a the case and landed in one of the circuits? – Rolnik – 2010-10-14T20:21:58.820

1In general, the same 'spring cleaning' that loosens up dust bunnies might help with some stray pieces of metal. – Rolnik – 2010-10-14T20:22:42.830

Try another hard drive. – Moab – 2010-10-14T21:42:08.217

Tell me more about – Rolnik – 2010-10-14T21:49:19.440

"power supply that I know works"... is it rated at substantially more Watts than the replacement, i.e., > 50% more watts? If not, I would hesitate to call it a 'known good' power supply. – Rolnik – 2010-10-14T21:50:45.503

@Moab: I don't have a spare hard drive, unfortunately. And like I said, MSHDD didn't report any issues and chkdsk worked fine when run from a Recovery CD. @Rolnik: I'll try cleaning it out thoroughly. As for the power supply, the current one is rated at 200W and the one I tried is rated at 400W. I pulled it out of a machine that I've been using for years with no issues. – David Brown – 2010-10-14T22:33:39.367

MSHDD does not detect all problems. Another thing to try is replace the data cable to the hard drive. – Moab – 2010-10-15T18:46:19.900