How To Manually Test a Power Supply With a

Multimeter
Unplug the power connectors from each and every internal device.

1 . Tip: An easy way to confirm that each power connector is unplugged is to

2 . Note: There is no need to remove the actual power supply unit from the
computer nor is there any reason to disconnect any data cables or other cables not
originating from the power supply.

3. Group all of the power cables and connectors together for easy testing.

As you're organizing the power cables, I highly recommend rerouting them and
pulling them as far away from the computer case as possible. This will make it as
easy as possible to test the power supply connections.

4. Short out pins 15 or black one and 16 or green one the 24-pin motherboard power
connector with a small piece of wire.

You'll probably need to take a look at the ATX 24 pin 12V Power Supply Pinout
table to determine the locations of these two pins.

5. Confirm that the power supply voltage switch located on the power supply is
properly set for your country.

Note: In the US, the voltage should be set to 110V/115V. Check the Foreign
Electricity Guide for voltage settings in other countries.

6. Plug the PSU into a live outlet and flip the switch on the back of the power
supply. Assuming that the power supply is at least minimally functional and that
you've properly shorted the pins in Step 5, you should hear the fan begin to run.

Important: Just because the fan is running does not mean that your power supply
is supplying power to your devices properly. You'll need to continue testing to
confirm that.

Note: Some power supplies do not have a switch on the back of the unit. If the
PSU you're testing does not, the fan should begin to run immediately after
plugging the unit into the wall.

7. Turn on your multimeter and turn the dial to the VDC (Volts DC) setting.
 Note: If the multimeter you're using does not have an auto-ranging feature, set the
range to 10.00V.

8. First we'll test the 24 pin motherboard power connector:

Connect the negative probe on the multimeter (black) to any ground wired pin and
connect the positive probe (red) to the first power line you want to test. The 24
pin main power connector has +3.3 VDC, +5 VDC, -5 VDC (optional), +12 VDC,
and -12 VDC lines across multiple pins.

You'll need to reference the ATX 24 pin 12V Power Supply Pinout for the
locations of these pins.

I recommend testing every pin on the 24 pin connector that carries a voltage. This
will confirm that each line is supplying the proper voltage and that each pin is
properly terminated.

9. Document the number that the multimeter shows for each voltage tested and
confirm that the reported voltage is within approved tolerance. You can reference
for a list of proper ranges for each voltage.

Are any voltages outside the approved tolerance? If yes, replace the power supply.
If all voltages are within tolerance, your power supply is not defective.

Important: If your power supply passes your tests, I highly recommend you
continue testing to confirm that it can operate properly under a load. If you're not
interested in testing your PSU further, skip to Step 15.

10. Turn off the switch on the back of the power supply and unplug it from the wall.
11. Reconnect all of your internal devices to power. Also, don't forget to remove the
short you created in Step 5 before plugging back in the 24 pin motherboard power
connector.

Note: The biggest mistake made at this point is forgetting to plug everything back
in. Aside from the main power connector to the motherboard, don't forget to
provide power to your hard drive(s), optical drive(s), and floppy drive. Some
motherboards require an additional 4, 6, or 8 pin power connector and some video
cards need dedicated power too.

12. Plug in your power supply, flip the switch on the back if you have one, and then
turn on your computer as you normally do with the power switch on the front of
the PC.

Note: Yes, you'll be running your computer with the case cover removed which is
perfectly safe as long as you're careful.
 Note: It's not common, but if your PC does not turn on with the cover removed,
you may have to move the appropriate jumper on the motherboard to allow this.
Your computer or motherboard manual should explain how to do this.

13. Repeat Step 9 and Step 10, testing and documenting the voltages for other power
connectors like the 4 pin peripheral power connector, the 15 pin SATA power
connector, and the 4 pin floppy power connector.

Note: The pinouts necessary to test these power connectors with a multimeter can
be found in my ATX Power Supply Pinout Tables list.

Just as with the 24 pin motherboard power connector, if any voltages fall too far
outside the listed voltage (see Power Supply Voltage Tolerances) you should
replace the power supply.

14. Once your testing is complete, turn off and unplug the PC and then put the cover
back on the case.

Assuming your power supply tested good or you've replaced your power supply
with a new one, you can now turn your computer back on and/or continue
troubleshooting the problem you are having.