Troubleshooting a PSU


Dec 19, 2012
I am in the process of upgrading my PC. I have a 500W PSU and case that I would like to reuse from an old build. Something is awry with the old build and I am trying to troubleshoot and basically make sure its not the PSU, the rest I dont care as much about. I am hoping someone here can figure out what is up or at least be certain the PSU is fine based on what I describe.

I have mobo, cpu, ram, and PSU hooked up "pseudo-PC" style like in Video card is DVI'd to a monitor. Everything is plugged in to power and the PSU switch is in "off" position. As soon as I flip the switch on the psu to on, boom, everything whizzes up, mobo LEDs come on and the fans on the GPU and CPU start turning. This is without me pressing any button on the mobo or shorting the circuit like in aforementioned video. It just comes on.

Something else of possible interest is the fact that after I turn the PSU switch to on, the "stand by" light on the PSU comes on instead of the "on" light.

Also, it wont post. Nothing happens except fans/leds coming on.

Is it my PSU? Or something else...

Here are the specs if it matters

GPU: 8800 GT 512 MB

CPU: Intel Core 2 Duo E6400 (2.13 GHZ)


MOBO: ABIT AW9D LGA 775 Intel 975X

Hard Drive: 250 GB 7200 rpm >.>

PSU: Thermaltake 500W
Case: Thermltake Tsunami
Welcome to Tom's Hardware Forums,
To properly test your PSU, you will want a Digital Multi-Meter (DMM) and a paperclip. The paperclip is to jump the PSU (so that it thinks it is plugged into a computer) and the DMM is then used to check voltages. This link explains the different connections found on power supplies and what voltages are found in the individual pins: All about the various PC power supply cables and connectors
This link explains how to jump your PSU with the paperclip: SeaSonic Power Supply Jump Start Guideline (direct link to a PDF file)
You want to measure all pins that have a voltage, ground and sensor pins shouldn't need to be checked. One thing you might also try, since your computer seems to start without additional input... See if the PSU will turn on without jumping the green and ground wire on the 24 pin. It shouldn't but then again, your computer shouldn't turn on without additional input
Hope it helps


Oct 28, 2007
As I dont have a multi-meter, I can currently only attempt the last test you mentioned. I just plugged the PSU into the wall and left everything else completely unplugged. When I flip the switch on the PSU the fan comes on and a faint whirring starts inside. Not entirely sure what this means.
If that was done without the 24 pin's green and black wires jumped, that means your PSU is not working correctly. When the rear switch is in the on position (I) without the 24 pin being jumped, the PSU's fan should not come on as it should only provide 5v standby power to the purple wire. Not enough of a load to start the fan unless the PSU is exceptionally dusty.
I'm going to recommend replacement of your PSU. Your specs indicate to me that no more than 350W is needed (if a high quality PSU) but you could go as high as 600W without getting into 'overkill'. Here is the cheapest replacement I would recommend: CORSAIR Builder Series CX430 $46 with shipping seems pretty good.
BTW, if the fan came on only when the black and green wires were jumped with a paperclip, ignore the previous
If you are going to upgrade you graphics card, that may require a little more wattage


Oct 28, 2007
Thanks man. Makes sense. Hey your "exceptionally dusty" comment intrigued me, as this thing has been sitting in a garage for a couple years. Which parts of the PSU being dusty might make something like this occur? If its a simple problem of cleaning the thing up a bit then I would rather do that then dropping the cash.

Also, I fear I made a mistake in posting my old specs, as that isnt too helpful when I am trying to use this PSU with a new build that I just ordered off Newegg last night.

Heres the new stuff. Does this change new PSU reccomendations?

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD Phenom II X4 965 Black 3.4GHz Quad-Core Processor ($89.99 @ NCIX US)
Motherboard: ASRock 970 Extreme3 ATX AM3+ Motherboard ($69.99 @ Newegg)
Memory: G.Skill Value Series 8GB (2 x 4GB) DDR3-1333 Memory ($37.99 @ Newegg)
Video Card: HIS Radeon HD 7850 2GB Video Card ($189.99 @ Newegg)
Total: $387.96
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-20 19:35 EST-0500)

Similar threads