How to Test a PC Power Supply with a Multimeter (Guide)

Published on: May 18, 2022 by Sam Orlovsky Learning Multimeter

A good power supply can make or break your pc, so it’s worth knowing how to properly test a power supply unit (PSU) with a multimeter properly.

Testing with a Multimeter

Testing your computer’s power supply is crucial when trying to diagnose computer issues and should be the first thing you do if you’re experiencing problems with your system. Thankfully, this is a fairly simple process that requires only some basic tools to complete. Here’s how to test the power supply of your desktop PC in just a few minutes so you can identify and fix any potential issues.

How to Test PC Power Supply with Multimeter (Guide)

A good power supply can make or break your system, so it’s worth knowing how to properly test a power supply unit (PSU) with a multimeter properly.

Testing with Multimeter

1. Check First the PC Repair Safety Tips

Before checking your power supply, make sure you have disconnected AC power from the computer and that you are properly grounded.

Safety should always be the first responsibility when working on a PC. To ensure safety while doing this process, it is crucial to follow some safety tips. First, wear an anti-static wrist strap to protect your computer’s components from static electricity. Make sure that there is no water or drinks around you. Also, keep all your tools away from where you are working with the computer because if you touch any of these items and then touch any internal part of the computer, you will short out (or even destroy) the motherboard or other parts in your system. (1)

2. Open your Computer’s Case

opening computer case — Video | GuruBrew

Disconnect all cables connected to the computer and remove its cover. You should see the power supply unit mounted inside the case. Find out how to remove its cover by reading its manual or looking at it closely.

3. Unplug the Power Connectors

Britec09 testing the power supply wires with multimeter — Video | Britec09

Unplug all power connectors except the PSU’s main power connector (20/24-pin connector). Make sure that there are no power connectors that are connected to any of the internal devices inside your computer (e.g., video cards, CD/DVD ROMs, hard drives, etc.)

4. Group All of the Power Cables

group all the wire connectors — Video | HealMyTech

Power supply cables are typically grouped together in one part of the case. This is for easy access and to reduce clutter within the case itself. When you’re testing your power supply, it’s best to group all the cables together so that you can see them clearly. To do this, you’ll want to remove them from their current position and place them back in an area that’s easy for you to access. You can use zip ties or twist ties to keep them neat and tidy.

5. Short the 2-pins 15 & 16 Out on the 24-pin Motherboard

computer motherboard — Video | GuruBrew

If your power supply has a 20-pin connector, skip this step, but if the PSU has a 24-pin connector, then you will have to short pins 15 and 16. To do so, you are going to need a paperclip or jumper wire. Keep reading, and I’ll show you how to short them out with a paperclip.

First, straighten out the paperclip as much as possible. Then grab one end of the paperclip and insert it into pin 15 on the 24-pin connector. Next, take the other end of the paperclip and insert it into pin 16. Once that is done, go ahead and attach the 24-pin connector to your motherboard. (2)

6. Make Sure That the Power Supply Voltage Switch

You will need to confirm that the power supply voltage switch is set for your local electrical system when you are setting up the power supply. If you live in a country where the standard outlet voltage is 110 volts, such as the United States, then you should have the setting on 110 volts. If you live in a country that uses 220 volts, like most European countries, then the setting should be on 220 volts.

Once you have verified that the voltage setting is correct, it’s time to gather your tools and supplies. You will need an electrical tester or multimeter to test the power supply. You may also want to consider wearing safety glasses and gloves during this process as well.

7. Plug the PSU into a Live Outlet

GuruBrew demonstrating how to test power supply with multimeter — Video | GuruBrew

If your computer isn’t currently turned on, plug it into an active outlet before beginning the testing process. This will ensure that there is enough power for the tests when they are performed. Note that if your PC still doesn’t turn on after testing the power supply, there may be other issues at play—but the power supply will still function properly and can be used in another PC or sold for parts.

8. Turn on your Multimeter

Set the multimeter to read DC volts. If you’re not sure how to do this, consult the instructions that came with your multimeter. Some multimeters have a switch for selecting AC or DC voltage readings, while others have buttons that allow you to set the function and range.

Plug the black probe into the COM jack on the multimeter. This is usually the jack that is labeled either “COM” or “-” (negative), and it will probably be black in color.

Plug the red probe into the V/Ω jack on the multimeter. This is usually the jack that is labeled either “V/Ω” or “+” (positive), and it will probably be red in color.

9. Testing the 24-pin Motherboard Power Connector for Continuity

To test the 24-pin motherboard power connector, look for the 20-pin motherboard power connector on your power supply unit (PSU). This particular connector has two distinct rows, each with 12 pins. The rows are offset and staggered so that all 24 pins correspond to the same socket on the PSU. More specifically, all 24 pins are set up in an alternating arrangement, where each row starts with a pin that shares its connection with the opposite row’s pin. Follow this pattern and then check if there is any visible damage to either rows’ pins or the motherboard’s 24-pin port. If there is damage to either of these two parts, we may recommend getting certified repairs from a local professional.

10. Document the Number that the Multimeter Shows

multimeter at 07.7 reading — Video | ESRepair

After setting your multimeter to DC Voltage, connect the red probe to the green wire, and the black probe to one of the black wires. Because there are several black wires, it doesn’t really matter which one you choose, but it’s best not to touch both probes together on the same wire as this could cause damage. Document what number shows up on your multimeter’s display—this is your “input voltage.”

11. Turn off the Power Supply, and Engage the Switch on the Back of its Supply Unit

Next, turn off the power switch on the back of the power supply unit that is connected to your AC outlet. Then disconnect all of your internal devices from their power plugs. Reconnect all of those devices once again and document what number shows up on your multimeter’s display—this is your “output voltage.”

12. Power up All of your Internal Devices

After testing your power supply, flip the switch off again and reconnect all of your internal devices to power. (CD/DVD drives, hard drive, graphics card, etc.), replace all panels as there’s no reason to leave everything disconnected for long, so reconnect all of your internal devices to their power sources, and you’re good to go!

13. Plug in your Power Supply

You can now plug the power supply into a wall outlet or into a power strip. It’s very important that there is nothing else plugged into the power strip or surge protector with your power supply. If there are other devices plugged in, they might cause problems with the test.

14. Repeat Step 9 and Step 10

Once again, turn on your multimeter and set it to its DC voltage range (20V). Repeat this process for all of the connectors that have a black wire (ground) and colored wires (voltage). This time, however, make sure not to touch any of the bare ends of the multimeter probes against anything when they’re inside the PSU’s connectors. Doing so could result in a short circuit or an electric shock if there are problems with what you’re testing.

15. After you Finish Testing, Turn off and Unplug the Computer

Once you have completed testing, turn off and unplug the computer. It’s important to unplug all of the components from your computer before you begin any type of troubleshooting or repair process.

Tips

The most important thing to remember is that the voltage, current and resistance readings you get will vary depending on the brand of multimeter you use. So, always read your multimeter’s manual before attempting this test.
Check all connections and make sure that the power supply is connected to the motherboard and all other components.
Make sure the power supply is on and there is no blown fuse or tripped circuit breaker.
Do not plug anything into the wall outlet while testing your PC power supply with a multimeter as this could damage both devices and/or cause injury.
If you have any doubts as to whether or not your PC’s power supply is working properly, consult your computer manufacturer for more information before proceeding with this tutorial.

Take a look at some of our related articles below.

References
(1) PC – https://www.britannica.com/technology/personal-computer
(2) motherboard – https://www.hp.com/us-en/shop/tech-takes/what-does-a-motherboard-do

Video References

Britec09

GuruBrew

ESRepair