Power Supply Testing

About two weeks ago, I posted this thread on problems with my wife’s desktop. I’ve tried a few things so far. While the total system hangs have seemed to stop, the random reboots have increased in frequency. I’m trying to figure out a way to test the current power supply, an Antec 350W, and had a few questions.

  1. Are the BIOS diagnostic utilities useful for isolating power problems? One screen reports actual voltage values for the +/- 5 and +/- 12 V leads from the power supply. All of the actual values are very close to the rated values, except the +12 V, which is reading between 10.0 and 10.5 actual values. Does this indicate problems with the power supply? Also, the Vcore reading seems to hover around 1.6V – is this normal?

  2. Can you use a multimeter to reliably test a power supply without having the supply connected to a motherboard under load? All the sites I’m finding state you need the power supply hooked up to a motherboard to test it, but I had a bookmarked site (dead now) that suggested you could test a supply just by plugging multimeter leads into various slots on the unplugged 20-pin power connector. I’ve got a multimeter, but I don’t feel comfortable trying to wedge the leads into a plugged-in power connector for testing. I was hoping there would be a way to test it without needing it plugged into anything except the wall outlet providing power to the supply itself.

Thanks in advance for any advice.

The reliability of BIOS readings is often suspect, but if most of them are close to what they should be, then it’s probably not too far off.

The Vcore will vary depending on what CPU you have, but 1.6V sounds reasonable. That 12V reading is waaay off, though. The allowed tolerance is +/-5%, so it should be 11.4V at the minimum.

I’m not sure about whether the PSU should be hooked to the motherboard or not when taking multimeter readings (readings with a load could be different from ‘open’ readings), but if you want to be safe and hook it up, you can still get readings of the 5V and 12V rails off of any of the molex connectors.

  1. Yes, a simple method of looking at it would be searching for power fluctuations… normally you will have a straight line graph if your power supply is working fine.

  2. You could try it, but it wouldn’t reflect the “real world” situation – that is hooking it up to a motherboard would naturally change the parameters greatly. Heck, maybe even the motherboard is at fault and not the power supply…?!

  3. You should also try Prime95, if you haven’t already. It’s an awesome tool that if you run it in “torture mode” will hint you may have problems like: bad memory, bad power supply, overheating, bad cpu, etc.

  4. Referring to #2, conceivably you could even be having a grounding issue. I’ve had that before and making sure my motherboard was not touching the case in odd places got rid of the problem.

I know this is pretty obvious, but have you tried hooking up her motherboard to a different power supply?

In my experience this sounds like a heat on the CPU issue. Especially if the PC is just sitting and reboots. Power problems typically end up causing failure of individual parts. So you’ll get blue screens and harddrives that won’t spin up. Not saying it isn’t possible, but in my experience I would look at the CPU, and if not that, try connecting another power supply.