How to Test the Computer Power Supply

Level of difficulty: Difficult

In a computer system, the power supply unit is responsible for converting the standard household electrical current to a low DC voltage that can be used by the machine during its operation and is responsible for powering up the different internal components of the computer. Normally, a common indication of a problem with the power supply unit is that its internal fan fails to rotate when powered up and the computer system does not receive any electricity. In some instances, frequent unexplained rebooting of the machine has been caused by a faulty power supply which is no longer capable of maintaining a constant flow of electricity to the machine. However, before running to the computer store or bringing the machine for a power supply replacement, testing it with a multimeter tester device will confirm whether or not the problem lies in the operation of the power supply unit.

Materials Needed:
- Multimeter
- power supply unit
- Philips head screwdriver
- computer
- grounding wristband
Step 1
The very first test to be performed is not on the power supply unit but on the electrical socket where the machine is plugged into. Visually inspect it to make sure that it is in good condition and is not the source of the problem. Alternatively, get a small lamp or clock radio and plug it into the socket to verify if it delivers adequate electricity.
Step 2
Get the multimeter and test the electrical socket to get a proper reading of its output. It should be approximately 120 to 240 volts depending on the standard voltage running in your household.
Step 3
Turn off the computer and unplug it from the wall socket. Before opening the case, make sure that you are properly grounded by wearing a grounding wristband.
Step 4
Remove the computer cover. Visually inspect the power supply unit and its connectors for any signs of damage or burn. Check also the sockets where the connectors are plugged in. These are normally on the motherboard, hard drive, floppy drive, CD or DVD drive, and auxiliary fans among others.
Step 5
Look for a power connector that is not being used. If none is available, simply unplug any connector used either by the hard drive or the CD or DVD drive.
Step 6
Get the multimeter and place it in the setting that reads DC voltage in the range greater than 12 volts. Plug the computer back into the wall socket and power it up.
Step 7
Hold the power connector (not the wires) and locate the black and the yellow wires. Insert the black probe of the tester to the hole corresponding to the black wire and the red probe corresponding to the yellow wire. Verify if the multimeter gets a reading of +12 volts.
Step 8
Keeping the black probe in its current position, move the red probe to the hole corresponding to the red wire of the connector. The reading should be +5 volts on the multimeter.
Step 9
If you get a different or no reading at all during the execution of Step 7 and Step 8, this confirms that the power supply unit has already gone bad and must be replaced immediately. If however, the readings are accurate, the potential problem may be coming from the computer motherboard.