Is your computer randomly shutting down or restarting? One possible cause of this problem is a failing power supply unit (PSU). Fortunately, you can test it using a multimeter in a few simple steps.
To test a power supply with a multimeter, disconnect the internal devices and cables. Open the PC case, create a short on the 24-pin motherboard power connector, and set the multimeter to VDC. Connect the multimeter red and black probes to the pins. Take the voltage reading to ensure they fall within the approved tolerance range. If not, replace the PSU.
To help you with the task, we’ve compiled a detailed guide to walk you through the step-by-step process of how to test a power supply with a multimeter to see if it’s the root cause of the issues.
- Testing a Power Supply With a Multimeter
- Step #1: Taking Precautionary Measures
- Step #2: Opening the Computer Case
- Step #3: Plugging the PSU Into the Power Supply Source
- Step #4: Setting the Multimeter
- Step #5: Taking the Multimeter Readings
- Step #6: Reconnecting the Internal Power Connectors
- Step #7: Retesting the Voltage
- Step #8: Placing the PC Cover Back
- Summary
Testing a Power Supply With a Multimeter
If you don’t know how to test a power supply with a multimeter, our following step-by-step method will help you get through the process without any issues.
Step #1: Taking Precautionary Measures
Before start testing the power supply with a multimeter, make sure to take the following preventive measures.
- Remove your USB devices or external drives.
- Disconnect all the cables.
- Disconnect external hardware and expansion cards.
- Remove the CPU and RAM and reconnect again.
- Clean and ventilate your PC.
Step #2: Opening the Computer Case
In the next step, power on your PC and make sure you’ve disconnected everything. Now, place your computer on a non-static flat surface and open its case. Flip the switch off at the back of the power supply unit and disconnect all internal power connectors.
Once you disconnect the connectors, group them with the power cables to organize them for easy testing. Connect pins 15 and 16 to the 24-pin motherboard power connector using a small wire.
You can use the table below to locate these pins on the motherboard.
| Pin No. | Name | Cable Color | Details |
| i | +3.3V | Orange | +3.3 VDC |
| ii | +3.3V | Orange | +3.3 VDC |
| iii | COM | Black | Ground |
| iv | +5V | Red | +5 VDC |
| v | COM | Black | Ground |
| vi | +5V | Red | +5 VDC |
| vii | COM | Black | Ground |
| viii | PWR_ON | Gray | Power Good |
| ix | +5VSB | Purple | +5 VDC Standby |
| x | +12V1 | Yellow | +12 VDC |
| xi | +12V1 | Yellow | +12 VDC |
| xii | +3.3V | Orange | +3.3 VDC |
| xiii | +3.3V | Orange | +3.3 VDC |
| xiv | -12V | Blue | -12 VDC |
| xv | COM | Black | Ground |
| xvi | PS_ON# | Green | Power Supply On |
| xvii | COM | Black | Ground |
| xviii | COM | Black | Ground |
| xix | COM | Black | Ground |
| xx | NC | White | -5 VDC (Removed in ATX12V v2.01 – optional) |
| xxi | +5V | Red | +5 VDC |
| xxii | +5V | Red | +5 VDC |
| xxiii | +5V | Red | +5 VDC |
| xxiv | COM | Black | Ground |
Step #3: Plugging the PSU Into the Power Supply Source
Set the power supply voltage according to your country at the back of your PSU.
Next, plug the power supply unit into a power outlet and flip the switch back on. If the fan starts to spin, continue with further steps.
However, if the fan does not spin, you must replace your power supply.
Step #4: Setting the Multimeter
In this next step, turn on the multimeter and set it to Volts DC (VDC) or 10.00V range. Next, connect the black probe of the multimeter with any black ground pins and the red probe with every pin having voltage on the 24-pin motherboard power connector.
The voltage supply in these pins will help confirm the power supply in them. The 24-pin main power connector has voltage lines for +3.3 VDC, +5 VDC, -5 VDC (optional), +12 VDC, and -12 VDC.
Step #5: Taking the Multimeter Readings
Record the multimeter readings and ensure that the tested voltage is within the approved tolerance, as shown in the table.
| Voltage Rail | Tolerance | Minimum Voltage | Maximum Voltage |
| +5VDC | ± 5% | +4.750 VDC | +5.250 VDC |
| +5VSB | ± 5% | +4.750 VDC | +5.250 VDC |
| +3.3VDC | ± 5% | +3.135 VDC | +3.465 VDC |
| -12VDC | ± 10% | -10.800 VDC | – 13.200 VDC |
| +12VDC | ± 5% | +11.400 VDC | +12.600 VDC |
| -5VDC (if used) | ± 10% | -4.500 VDC | -5.500 VDC |
Your power supply is not defective if the voltage is within the tolerance level. But, if any voltages are outside the range, you’ll need to replace your PSU.
Step #6: Reconnecting the Internal Power Connectors
Now, disconnect the PSU from the power outlet, and remove the short you created earlier with the 4-pin motherboard power connecter.
Reconnect all the internal devices and flip the back switch to turn on your power supply.
If your PC doesn’t turn on with the cover removed, you may have to adjust the corresponding jumper on the motherboard to enable this function. Your computer or motherboard manual should have instructions on how to do this.
Step #7: Retesting the Voltage
In this step, you have to repeat the steps to test the voltage of other power connectors, such as the 4-pin peripheral power connector, the 15-pin SATA power connector, and the 4-pin floppy power connector, to ensure it falls under the approved tolerance level.
You must replace the PSU if the recorded value falls too far from the tolerable limit.
Step #8: Placing the PC Cover Back
Once you test the PSU and resolve the issue, switch it off and put the cover back on your computer case.
Finally, turn on your computer and see if the issue still exists.
Summary
In this article, we’ve discussed how to test a power supply with a multimeter to see if the PSU is causing an issue on your PC.
Hopefully, this article helped resolve your query, and you can now test your PSU without much effort.
