Dead PC Diagnosis Filter - am I on the right track?

November 4, 2007 9:40 AM

Dead PC Diagnosis Filter - am I on the right track?

Today my desktop PC when "phut" and died. (Actually, I had my headphones on at the time, and so I don't know what noises it made prior to, or at the time of death.)

Anyhow, it's a self-built machine - I've been building my own machines for about 20 years now (and am normally better at diagnosing faults than I'm feeling today). Quick spec: Intel Dual Core CPU, Asus P5W DH Deluxe motherboard, ATI X1950 graphics card, mix of hard drives, etc.

Machine died unexpectedly. There was a smell of burning. The nose test indicated the smell came from the PSU, but heck, I'm not a sniffer dog, so that might be wrong.

Now I switch the machine on, no fans turn (including the fan in the PSU) (both case and CPU fan powered from motherboard), and no drives spin up. An LED on the mainboard lights, and an LED on the graphics card. If I press eject on the CD drive, its light turns on briefly, but it doesn't eject.

So, there's definitely some power around somewhere, but here's where I start to get hazy with my diagnosis. As I understand it, ATX PSUs supply 2 voltage circuits - a 12v and 5v one. Am I on the right track thinking that the 12v circuit has died in the PSU, otherwise, I can't see why there is some power to the mainboard and beyond, but no drive or boot activity. (No POST beeps either, btw...)

I have no other power supplies or PCs here to test any further, so before I go out tomorrow to buy a new PSU, can anyone tell me if I'm barking up completely the wrong tree?

posted by benzo8 to Computers & Internet (6 answers total)

Sounds like a bad PSU to me.
posted by rmtravis at 9:48 AM on November 4, 2007

Echoing the PSU most likely being toast. Problem is that if your PSU did bite the dust, it could have easily burnt out your motherboard or other components in the process.

Your MB may also be the culprit. For ATX's, the front panel switches on the power supply through your MB, so if the MB's not working correctly, it won't know how to turn on your power supply.
posted by jmd82 at 10:09 AM on November 4, 2007

Best answer: In the power supply, +5Vsb voltage is often generated independently from the main switching circuit..

To know for sure, test the power supply while it isn't connected to the system at all.
posted by Chuckles at 10:43 AM on November 4, 2007

Here is a schematic of an ATX supply, you can see the +5Vsb circuit at the middle bottom, very much separate from the other power supply outputs.

I used to have a much better link, with a complete walk through of the entire circuit, written for a PC enthusiast audience..
posted by Chuckles at 10:53 AM on November 4, 2007

Sounds like the PSU. I recently had one die on me after only a month and the behavior was very similar, absent the smell.

I didn't have the means to test the power supply so I just pulled it out and took it to a little computer repair place nearby and they tested it for me for free.
posted by camcgee at 7:36 PM on November 4, 2007

Response by poster: Thanks all - you reassured me that I was on the right track, a new PSU was purchased and installed this morning and everything's fine once again...
posted by benzo8 at 2:58 AM on November 5, 2007