How to Manually Test a Power Supply With a Multimeter
Testing a power supply manually with a multimeter is one of two ways to test a power supply in a computer. A properly executed PSU test using a multimeter should confirm whether the power supply is in good working order or should be replaced. 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’re having. To make testing your PSU easier, you should also move your disconnected and open computer case somewhere easy to work, like on a table or other flat, non-static surface. An easy way to confirm that each power connector is unplugged is to work from the bundle of power cables coming from the power supply inside the PC. Each group of wires should terminate to one or more power connectors. As you’re organizing the cables, we 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. 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. Some power supplies don’t have a switch on the back of the unit. If the PSU you’re testing doesn’t, the fan should begin to run immediately after plugging the unit into the wall. 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. We 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. Are any voltages outside the approved tolerance? If yes, replace the power supply. If all voltages are within tolerance, your power supply isn’t defective. It’s not common, but if your PC doesn’t 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. Just as with the 24-pin motherboard power connector, if any voltages fall too far outside the listed voltage, you should replace the power supply.
