How to Test a Computer Power Supply With a Multitester

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A faulty power supply can cause a computer to function irregularly, or in some cases, not at all. Some of the potential problems that can result from a faulty power supply include the computer not powering up, the PC freezing during boot up or the PC randomly shutting itself off. Each of these cases can be a true headache for the user--so having the ability to test the power supply could not only save you from experiencing too much computer downtime--it could also save you the cost of purchasing an entirely new machine. Here is how to do it with a multitester.

Things You'll Need

  • Digital Multimeter
  • Computer
  • Check the quality of the receptacle and/or power strip your computer is plugged into (this is the first test you should always perform). Set the multimeter to read voltage and test the receptacle or power strip to ensure that the voltage is reading properly. Your tester should read approximately 120 volts.

  • If the receptacle is good, the next thing you will have to do is turn off your PC and open your computer's case. Depending on the make and model, that can be a chore in and of itself, but you can always check your documentation that came with the machine for guidance.

    Leave the PC plugged into the wall outlet, but keep the machine off.

  • With the case open, locate your power supply. It is a large, silver metal box with many colored wires coming out of it.

    Before you put your hands into the CPU box, be sure to ground yourself by touching something metallic or by grounding yourself to the box itself using a grounding wristband that you can purchase from your local office supply or computer store.

  • Locate a power connector that isn't being utilized. If they are all in use, just unplug the one that is plugged into the back of the hard drive or one of the CD drives.

  • Set your multitester to read DC voltage in a range greater than 12 volts.

    Turn your computer on.

  • On the power connector, look for the black and the yellow wire. Touch your tester's black probe to where the BLACK wire is connected to on the connector and the red probe to where the YELLOW wire is connected. Your multitester should read +12 volts.

  • Keep your black probe in its current position and touch the red probe to where the RED wire is located on the connector. Your digital multimeter should now read +5 volts.

  • If you get a different reading or no reading, then the power supply is bad and should be replaced. If you get the proper reading on your multitester, then your motherboard may be the cause of your PC's problems.

Tips & Warnings

  • Always ground yourself before working inside your computer.
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