PSU: +5V rail problems?

[_xxx_]

Whenever I start a game and play for a few minutes, the system will just lock up. The sound keeps on playing as usual, just the picture is still and I can't do anything but reboot.

My first suspect was the PSU, so I installed MBM and made logs with voltages. The 12V rail is rock-solid, no fluctuations whatsoever, but the 5V rail seems to go down to 3.8V sometimes, though I couldn't relate that to the lockups, since that happens all the time it seems.

Can this lead to such a behaviour? Anyone had any similar experiences? I know the gfx-card usually puts a big load on the 12V rail, but I never heard of any problems related to the 5V rail.

And I also don't really trust MBM, since I had to set it up manually (my board is not in the database).

I'll be buying a new PSU today for my upgrade anyway (X1800XT and a new mobo), but I wanted to re-use this one for a second gaming PC I'll be building...

EDIT: all the components except for the PSU are new and have been tested in other machines with no problems whatsoever

 

[maaoouud]

You're quite right in not trusting mbm. Monitoring software is known to be rather inaccurate, however they might give a good indication of the ripple on the powerlines.

I think the easiest way to be sure is to buy a cheap multimeter (there's perfectly fine ones for €10) and just check the ripple yourself.

Older motherboards put a heavy strain on the 5V rail(s), but with newer the heaviest load has been moved to 12V. I've got an "old" psu that has a very good 5V rail at 40A and it still drops somewhat with heavy loads, but that does not mean it will make the computer unstable as the components should tolerate it as long as the ripple is within the ATX specifications.

Excessive ripple on the rails is a very common factor for instability so your problems was probably the psu.

 

[_xxx_]

Good idea with the multimeter, haven't thought of that. I'll see if I can get one tomorrow, thanks!

But onr thing bother me still, how do you explain the lockups and the sound still playing on? Shouldn't it also be locked up in a loop or such? Hmmm...

 

[_xxx_]

Ok, so it was indeed the PSU. The 5V rail fell down to ~3V at times. Damn.


But at least the new system is already up and running like a charm

 

[MPI]

I had the exact same problem recently, but only at start-up. After the n:th try the board finally booted. Checked with multimeter and it was 4,5V at cold start, and slowly rising to 4,75 or so when finally getting to the BIOS. Got a new PSU and everything's fine again. Although that sucked IMO, as the original was quite expensive and I planned to use it for a while... :-/

I'm amazed that your harddrives and such worked at less than 4V, though!! My drives made a curious sound when the voltage was as low as 4,5V...

 

[_xxx_]

Well, when the machine crashed HD's were spinning randomly although there was nothing running, so I guess these were also hit by the low voltage. I just forgot to mention that above.