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I'm trying to diagnose whether my computer has an ample power supply. Sometimes when I play a video-intensive game, both monitors lose the video signal, even though the computer remains on and sound playing. A theory I have is: the video card isn't getting sufficient power. I can't imagine it's overheating because the machine is well-ventilated and the video card isn't hot to touch when this happens.

Anyway, in my PC's BIOS there's a Hardware Monitor page, and among other voltages reported (such as CPU, DRAM, South Bridge, etc.) I can see the following values:

3.3V    3.152V
5V      4.944V
12V     11.872V

Are those the voltages used by peripherals? What voltage should I be referencing if I want to know what my video card (PCI Express) is consuming?

What is the normal range of values reported for those? My values above appear to be under by approximately 4.5%, 1.1%, and 1.1% respectively. Is that cause for concern?

How else should I be determining if my power supply is "right-sized" for my PC and video card, or am I perhaps barking up the wrong tree?


I purchased a new power supply: a 950W Enermax (providing me with more than enough power for even what will come next in my PC :-) The new voltage readings in my BIOS are now:

3.3V    3.236V
5V      4.992V
12V     12.096V

These are much closer to the ideals than the previous power supply.

Did this solve my problem? Well, no. :-/ So, now I'm suspecting the video card is at fault. The last time after it blanked out and I rebooted right away, I got a message on screen before POST telling me that I need to plug the power extension cable into the video card. It was plugged in.

So, I'm thinking the video card is at fault and periodically losing power due to a bad connection or what not. The video card is next on the list to replace, and now that I have a beefy power supply, I'll be getting a much better video card. :-D

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Read superuser.com/questions/132730/… –  Hello71 Jul 11 '10 at 21:28

1 Answer 1

up vote 4 down vote accepted

The supply rails have the same voltage across the entire system. Adding load will reduce it, but it will reduce it everywhere. Having said that, the 3.3V rail does seem just a bit low. 4.5% is barely within tolerances. Another problem is current, measured in amperes. If a circuit isn't getting enough current then it could cut out completely. There's usually no way to specifically measure current, short of sticking an ammeter in the way.

What you can do is monitor the voltage on the supply rails as you use the machine, and if you see one of them drop too low (a 5% drop is considered "too low") then get a better or larger PSU.

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