PSU - Very Low 3.3v = Bad PSU is the culprit?

[Khrovix]

I was trying to diagnose my brother's failing PC and I think it has become pretty obvious what the problem is, but I want to make sure before wasting money on parts.

PC was fine for 6-8 months of off and on use, but the last week or so he started encountering the 'will not post' issue, but only sometimes - it would start up and run fine after powering it off and on a few times to get it to post, but then it wouldn't post at all.

After running through various troubleshooting check lists (here and elsewhere) to narrow down the issue, I was about to blame a failed motherboard, but I then ran a check with a multimeter on the PSU connector wires.

I checked the wall socket and the power cord and they were fine. However, with the system breadboarded and powered on, but still not POSTing, I tested the PSU connector wire and found that the -12V and +12V were as they should be, but the +5V wires were running at about +4.7V and the 3.3V wires were only running at 0.52V. Yes, half a volt on all 3 orange wires instead of 3.3V.

This told me that it had to be the PSU that was bad and not the Mobo as I previously thought. Would this be a good conclusion?

Just to be clear on this, those 3 orange wires all measuring half volts instead of the 3.3V that they should, and the several red +5 all measuring in at about +4.7V definitely means he needs a new PSU, correct?

Thank you for any thoughts on this.

 

[Deathcon51]

While a lot of the issues point toward a faulty PSU, try a couple things:

- Find another power cable (maybe form your monitor) and plug that into your PSU.
- Unplug the whole PSU from the wall outlet and drain all the power (hold power button)
- Take out the CMOS battery

Your PSU only uses as much as the computer needs, if you run a 1250Watt PSU, but your system is only using 500Watts, then the PSU is only using 500Watts. It is likely that you have a faulty PSU though.