Strange Power Issues with Gigabyte GA-G31M-ES2L

[whusterj]

I am working with an older build and encountering a strange power issue. The computer will run fine after pulling all components, clearing CMOS, and re-installing components one-by-one, but then it becomes completely unresponsive (no fan spins) after leaving it powered off overnight. I have repeated this process a couple times now. I have rebuilt the board inside and outside of the case with the same results.

I am going to pick up a case speaker, but I do not have one with me right now to listen for error beeps.

I do not have a voltage tester for the PSU, but I'm reasonably certain this is not the issue, because the computer will run perfectly fine for 8+ hours after rebuild and all voltages look okay in BIOS.

The specs:

Gigabyte GA-G31M-ES2L MB
Core 2 Quad Q9550 2.83Ghz
EVGA GeForce 9800 GTX 512MB DDR3
2x Corsair Dominator 2GB, 1066Mhz (XMS2-8500)
2x Seagate 512MB HDD
Thermaltake 650 Watt PSU
Cooler Master 650 Watt PSU

Any hunches? Is there some "feature" of this Motherboard that might be calling this? When I had it working yesterday, I changed the BIOS "AC Back Function" to "Full On," but this does not seem to have changed anything.

Thanks.

 

[GearUp]

If the computer is unplugged for long periods the CMOS battery will degrade but it sounds like your PSU. Capacitors are essentially batteries and have less cranking power when cold and old.

 

[whusterj]

If the computer is unplugged for long periods the CMOS battery will degrade but it sounds like your PSU. Capacitors are essentially batteries and have less cranking power when cold and old.

Interesting idea about capacitors. I inspected all the MOBO capacitors and none appear to be bulging or leaking. A couple capacitors near the CPU were caked in dust. It may be coincidence, but after clearing away the dust, the computer booted up on the next try. It is now running fine once more, but only time will tell if it will boot again tomorrow.

I have been alternating between the two 650W PSUs mentioned in the original post. I thought the Cooler Master was dead, but tried it again on a whim and it's now powering the board just fine.

The CMOS battery is OLD, but it is remembering BIOS settings changes, and besides that, I have been able to boot without it a couple times, so I don't think that's the culprit.

So it seems to me it could be a bad capacitor, short, or other power issue on the MOBO. If it refuses to boot again, I will see if I can find and try out a new MOBO.

 

[GearUp]

I'm running one old system with a newer low-level graphics card (240GT). It rejected (8600GT) or ran less well (old 9600GT) with cards having slightly better performance index scores.
I haven't found any confirmation but suspected a spider web in some problems long ago.
For me power supplies either work or fail totally. Some of the capacitors in my power supplies have very slight bulges. If they were in a monitor it would be an indicator for replacement.