Perform a Computer Power Supply Test

A computer power supply test is a necessity if you are getting random computer crashes and really don't know where to start looking.

Some power supplies are really easy to diagnose, yet others can just way more problematic.  We'll look at a couple of different tests here to help isolate whether the computer power supply is the problem. or if it's something else in your computer.

If you're computer simply doesn't power on and you have a multimeter, this computer supply test will tell you if your power supply needs to be replaced.  To begin, simply remove the computer power supply from the computer case, you'll need a small piece of wire or a paper clip to power on the power supply manually.

A word on safety.  If you have a multimeter, you already should know how to use one, be careful.  We will be dealing with live current here, although low DC voltage, please exercise caution here.  If you don't have a multimeter, you may just want to pick up a PC power supply tester since they're really inexpensive.

24 Pin ATX Power Connector

To identify which side is what, the clip that locks this connector onto the motherboard is on numbers 13-24.

13	14	15	16	17	18	19	20	21	22	23	24
1	2	3	4	5	6	7	8	9	10	11	12

The table below will show you what each number should be when you perform your computer power supply test.  All volts are in DC.

1. 3.3
2. 3.3
3. Ground
4. 5.0
5. Ground
6. 5.0
7. Ground
8. 5.0 (Power okay signal to motherboard)
9. 5.0 (Standby trigger)
10. 12.0
11. 12.0
12. 3.3
13. 3.3
14. -12.0
15. Ground
16. Power supply on trigger (connect to a ground to turn on the computer power supply)
17. Ground
18. Ground
19. Ground
20. Empty or -5.0
21. 5.0
22. 5.0
23. 5.0
24. Ground

20 Pin ATX Power Connector

To identify which side is what, the clip that locks this connector onto the motherboard is on the 11-20 side.

11	12	13	14	15	16	17	18	19	20
1	2	3	4	5	6	7	8	9	10

The table below will show you what each computer supply test voltage should be. 
All volts are in DC.

1. 3.3
2. 3.3
3. Ground
4. 5.0
5. Ground
6. 5.0
7. Ground
8. 5.0 (Power okay signal to motherboard)
9. 5.0 (Standby trigger)
10. 12.0
11. 3.3
12. -12.0
13. Ground
14. Power supply on trigger (connect to a ground to turn on the computer power supply)
15. Ground
16. Ground
17. Ground
18. -5.0
19. 5.0
20. 5.0

Now that you know what each voltage should read, you'll need to connect the power supply on trigger to a ground to turn on the power supply and begin your computer power supply test.  Simply connect the two with a paper clip or a short piece of wire to begin your computer power supply test.

Turn the multimeter to DC volts and begin testing.  Although all of the voltages will fluctuate a bit, they should be very close to the table above.  About 10% tolerance is okay, 3.3 could be anywhere in between 3.4 and 3.2 volts and you shouldn't have any problem with your computer.

If all the voltages are but you still are experiencing some system trouble, let's look at other possible ways to tell the power supply is needing replacement.

• If you are overclocking your computer and your power supply is less than 500 watts, I recommend a bigger power supply, at least 650W for anything with only 1 video card, for 2 video card, 800W or bigger.
• If you push the power button on the computer and it doesn't come on, or you have to push it multiple times and it doesn't respond.
• Your system crashes the won't start back up immediately.
• On a monitoring utility, when your PC goes to full load, the voltage drops on the CPU by more than 0.2 volts.
• You run a computer with more than one hard drive, one video card, one dvd-rom, one floppy disk drive and your computer power supply is under 500W.  You need to get something bigger, not only will this make your computer more reliable, a bigger power supply is more energy efficient than one that is working just to keep your cpu on.

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