PC just shuts down

kensuguro · Post by **kensuguro** » Mon Jan 01, 2007 1:51 pm

Got a strange situation that's got me stumped. Since new years, my pc shuts down (immediate power down) and I need to unplug, and wait to power up. I don't know how to recreate it.. but it's strange that I need to unplug to get it to power up. Just throwing the question out for some hints.

Post by **garyb** » Mon Jan 01, 2007 3:22 pm

power supply is my guess...

braincell · Post by **braincell** » Mon Jan 01, 2007 3:25 pm

I was thinking that before I read Gary's comment.

kensuguro · Post by **kensuguro** » Mon Jan 01, 2007 6:00 pm

is there any way to diagnose PSU health?

Post by **garyb** » Mon Jan 01, 2007 11:40 pm

possibly the psu is filled with dust and is over heating? i think the best way to test it, is to replace it, sorry.

you could monitor voltages, but i doubt you'll see anything before it shuts down. when it shuts down, the monitoring is disabled...

i suppose something could be failing on the motherboard. astroman likes to point out that caps often fail, likewise caps are a big part of the powersupply. they're worth inspecting. the big caps in the power supply can be heavy enough to break loose when transported, you might check this if you like to solder. the thing's digital though, microcircuits are prone to intermittant, then catastrophic failure(or just unannounced death). an analog circuit usually degrades first and can be more easily monitored.

astroman · Post by **astroman** » Tue Jan 02, 2007 3:11 am

regarding electrolytic capacitors: there's a kind of 'gel' inside to increase capacity (simplyfied) while reducing space. This substance is fairly heat sensitive, that's why you (should...) find special 120-degree-centigrade types in (hot) locations like PSUs or near voltage regulators.
Since those caps are at least twice as expensive (a typical PSU has about a dozen of them), it's a significant cost factor.
My fanless PSU had the whole 'team' blown up recently because a cooler metal wasn't fixed properly... (not by me btw) and those were high speced caps.

The wearout of the 'gel' substance is unavoidable under whatever circumstances, heat simply accellerates the process.
So electrolytic caps are the first items to check on any gear beyond a certain age that seems to have a problem. In 'vintage' hi-fi people often don't bother but just replace all caps for simplicity sake (if the device is worth the effort of course), as a broken cap 'in circuit' can be difficult to measure sometimes.

Anyway, in this case I'd rather guess it's the power-on-off logic which is (afaik) controlled by the bios, but also by the OS via all the advanced-power-I-dunno-what... that leaves me a bit clueless

cheers, Tom

kensuguro · Post by **kensuguro** » Tue Jan 02, 2007 5:24 pm

hmm.. stuff like this is really hard to pinpoint since I can't recreate it, and it hasn't happened since the 2nd time..

Shroomz~> · Post by **Shroomz~>** » Wed Jan 03, 2007 11:08 am

I'd agree that it's most likely a faulty PSU, but I did have similar problems when an nvidea gfx card slowly died a few months back. My guess is that a combination of heat from the dsps & gathering of dust on the gfx card through static just proved to be too much for it, although the card was about 2/3 years old, so who knows.

Shroomz~> · Post by **Shroomz~>** » Wed Jan 03, 2007 11:48 am

Ken, another problem which might cause the symptoms you describe is a PCI card which is not seated properly for some reason. Although in my particular experience of that problem, the card in question just fails to work suddenly & won't work properly (even if re-seated) until the mobo is reset (PSU is unplugged then plugged back in).