Testing standard power supplies

[Redo40]

Check out Hpro's post for bridging instructions, then take a voltmeter or multimeter and check the voltages for each connector.

Put your black voltmeter lead in one of the black molex connector places, then place the red voltmeter lead in the red molex connector to read the 5 volt circuit. To read the 12 volt rail, leave the black voltmeter lead in the black molex connector and move the red voltmeter lead to the yellow molex connector.

Be sure your voltmeter is setup to read DC voltages instead of AC. Don't leave your meter set to the ohms or amps selection to try to read a voltage.

Red = 5 volts.
yellow = 12 volts.
Orange = 3.3 volts
Green = A control wire, Power Supply on.
Blue = -12 volts (note...minus sign)
Grey = A control wire, Power good circuit
White = -5 volts (note...minus sign)

Note this is for standard psu and only test the psu at idle, not under a load.

[Redo40]

Testing the PSU under load:

To properly test the PSU the voltage readings need to be taken directly off the motherboards 20-pin ATX connector using a good digital multimeter. To do so, first the power supply needs to be plugged into the rest of the system, as it normally would be. This will help to make the reading more precise in a real world environment. After the system is hooked up and powered on, get the digital multimeter out. Place the red probe on the corresponding wire on the back of the 20-pin ATX connector. Red is the 5v rail. Yellow is the 12V line. Orange is the 3.3V line. For a ground, use any of the black wires located on the 20-pin connector. You can take these readings off the auxiliary 6-pin connector or a 4 pin Molex.

Full load can be simulated by running a benchmark or something very intensive on the computer. Make sure to check the voltage and the fluctuations in the line. If the voltage reading goes up and down a lot at either idle or load, then the power is not supplying “clean” power. Fluctuations like this are not good and can cause problems.

Be aware that connecting a bad power supply to your computer can damage other parts of the computer. I suggest trying this on a test machine put together with older parts you may have lying around.

[morriswindgate]

For about 16 bucks you can also by a PSU tester that will quickly give you the condition of the PSU without potentially damaging anything.

[mike breck]

Yes, the easy way is to use an Antec PSU tester.

However, it is useful for people to know the classic way of doing it - especially testing the PSU under load.

Nicely explained Redo40.