Broken motherboard or PSU?

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System is an

Asus P5W DH Deluxe motherboard (ATX 12V 2.0, i.e. 24pin+4pin power
header) with E4500
Antex 380W supply. (ATX 12V 1.x i.e. 20pin + 4 pin type)
2 SATA drives, 1CD
GeForce 7300GT

The system has been running quite happily until a few days ago when my
wife reported a smell of burning plastic from the computer. When I
boot up now the computer follows one of the following sequences

1) PSU switch on, everything else off (so effectively in standby
2) Wait for 20 seconds plus
3) Power cuts out (green led goes off). Doesn't always happen, but
maybe I'm just not waiting long enough
4) Turn PSU switch off
5) green led flicks on briefly, and I hear a sound like a capacitor
discharging. I don't know if this is normal! I don't think I've seen
it before, but I don't normally spend that long looking at the
motherboard led....

1) PSU switched on. Hit the front power switch
2) Computer boots up as normal for between 2 and 20 seconds. I can use
the USB keyboard to enter the BIOS settings, or boot from HD, and
everything that should work, works, so far as I can test it.
3) power cuts out
4), 5) as above

This suggests to me that the problem lies with the PSU and not the

a) I don't have another PSU. I do have a multimeter. What can I do to
get a good degree of confidence that the fault lies in the PSU (or
not, as the case may be)?
b) What might have caused this problem in the first place?

Re: Broken motherboard or PSU?

Nutkey wrote:
Quoted text here. Click to load it

Some of that generation of Antec supplies have a leaking capacitor
problem. I have a "True 480W" sitting in my junk pile, which has
four leaking caps in it. I could hear a muffled "arcing" sound
just after startup. I removed the supply before anything nasty happened.
The "arcing" sound seems to disappear after the parts have warmed
up a little, but it doesn't mean the thing is happy.

As long as the supply is out of warranty, you can open it up for a look.
(They may cover one screw with a "warranty void" sticker, and you'll have
to remove the sticker, to be able to take the top off the supply.)
For safety, don't touch anything in there, just look at it. You'll likely
see some of the output side capacitors with an brown-orange deposit on top,
where the capacitor has bulged, split along the pressure relief
lines, then oozed out electrolyte. The reason for this, plus a picture,
are available in this article.

Try another supply and maybe you'll be back in shape again.

My True 480W supply did not have a lot of service hours on it. It sat
in a computer in storage for a couple years, and was in that sad shape
when I next tried it. So the breakdown of the capacitors, isn't even
related to abuse - just sitting in storage is enough incentive for the
bad chemistry inside.

Antec doesn't make their own supplies. They contract them out. My bad
one could have been made by ChannelWell (CWT). You may see a notation
on the transformer that indicates the OEM origin.


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