How to Test a Power Supply Using a Multimeter
Testing your power supply needs to be done when you suspect a malfunction. One of the simplest ways to do it is by using a multimeter. This is the manual method of testing a PSU as opposed to purchasing a power supply tester that can automatically detect problems.
If you do it correctly, this test will confirm for you whether it’s time to replace the PSU or if the unit works as it should. Keep in mind that not everyone should attempt to do this test. It’s recommended only if you’re experienced in doing electrical tests as it can be quite dangerous if you’re not very careful.
Assuming you already have a multimeter at your disposal, let’s see which are the required steps for executing this test. You can expect the test to need somewhere around 30-45 minutes of your time, perhaps more if you want to be more thorough.
1. Make sure you’re aware of the best safety measures
- As this process involves a certain level of danger, it’s mandatory to be familiar with the safety procedures when repairing computers. Some of the most critical points you need to be aware of are:
1. Power off completely
- This may seem obvious to most people, but it’s important to stress out that you should always flip the power switch off before attempting to repair a computer. And while you’re at it, unplug the computer as well for some extra peace of mind.
- When you pull the plug to start repairing the PC you need to wait a few minutes. There are miniature electronic components called capacitors that can still retain an electric charge. Even if the storage duration is quite limited, it’s better to be safe than sorry.
2. Weird smells and smoke
- Burning smells are always a sign that you should immediately take action. Together with seeing smoke coming from the case or anywhere else, these are indications that you need to pay close attention to. When a component gets damaged, you need to allow the whole computer to cool, then quickly find the issue and resolve it. This is usually done by doing a replacement for that part.
3. Never wear hand jewelry
- When working with high-voltage devices make sure you always take off your metal rings, bracelets, and any kind of hand jewelry beforehand. This is particularly important when testing the power supply as you can get electrocuted from anything conductive like that.
4. Know when it’s time to stop
- If during your repair work you discover a label telling you the part is not serviceable, then it’s very important to leave it as that. Don’t try to overlook this statement because there are many PC components which simply can’t be repaired, sometimes not even by professionals. Dangerous and highly sensitive parts, in particular, will present this warning.
2. Open the case
- With the computer off and all the cables unplugged, take the PC tower somewhere more comfortable to work and start opening the case. You’ll probably need a screwdriver for this.
3. Unplug the power connectors
- Make sure all the power connectors are no longer plugged in for every internal component inside the case. You can confirm that a certain cable has the role of a power connector by tracing it to the power supply inside the computer. Data cables can be left alone and taking out the PSU is also not required.
4. Keep the power cables organized
- It’s recommended to reroute and take the power cables to a different place away from the case. Maintaining them organized will simplify your work when it’s time to test the connectors.
5. Find the pins 15 and 16 on the power connector of the motherboard
- You will need to determine the locations of these pins because then you’ll have to short them out. In this testing, we’re working with a standard ATX motherboard. Check a pinout table like this one if you can’t find them.
6. Check to see if the PSU voltage switch is correctly set
- US users should have the switch set to 110V/115V, but you will need to find this information for your specific country if you live someplace else. This guide should help you in that regard.
7. Plug the PSU in
- Now it’s time to connect the power supply to a live outlet. Ensure that you set the power switch on (if there is one in the back). You should hear the fan start running if you’ve correctly shorted the pins. This is a good sign, but it’s not enough to consider it fully functional.
8. Turn the multimeter on
- Activate your multimeter and set the dial to Volts DC. The range must be set to 10.00V if your device lacks the auto-ranging feature.
9. Test the 24-pin power connector
- In this step, you have to connect the black and red probes to a ground wired pin and the power line you were planning on testing, respectively. Once again use the table in this link as a reference to find the location of the 24-pin motherboard main power connector and its lines.
- It’s recommended to test every pin with a voltage on the connector because you need to properly check if the lines deliver the correct voltage. It’s also essential to ensure that each pin is terminated as it should.
10. Document the multimeter values
- For each voltage you were testing you will need to note the number and then verify that is not under or over the specific voltage tolerance. Look at the third table on this link for reference regarding the correct ranges for each voltage.
- If you find out that certain voltages go over the maximum tolerance, then it means the PSU needs to be replaced. If there are no issues and the voltages stay within tolerance, you’ve got a functional power supply.
- Although you could stop right here with the testing, it’s strongly recommended to continue to see how the PSU operates under a load. This could be important to confirm that your power supply is fully functional. If you decide to do so, here’s what you need to do next. If not, you can skip the following steps and go directly to Step 14.
11. Turn off the PSU and unplug it
12. Connect back all the internal devices to receive power
- Here it’s important to make sure that everything (hard drives, video cards, other drives, etc.) is properly reconnected, but not only that. Be careful to remove the previously created short when inserting back the motherboard power connector.
- Plug in the power supply and turn on the computer normally
13. Test and document as in the previous steps
- We’ll do the same voltage testing process, but this time we’ll analyze other power connectors like those from various devices such as the SATA and peripheral connectors. To find the correct pinouts, it’s necessary once again to look in the pinout tables.
14. Complete the testing
- If the power supply passes all the tests, then you’ve confirmed it’s functional, so you can turn the computer off and reattach the cover on the case. There’s also the possibility that you need to make a replacement. In that case, turning the computer back on will have to wait until you find a new suitable PSU.
- You can also resume the troubleshooting process for the computer problem you were experiencing now.