How to manually check the computer source with a multimeter

Checking the power manually with a multimeter is one of two ways to check the power in your computer.

A properly performed PSU test with a multimeter will confirm that the computer power is working well or needs replacement.

These guidelines apply to standard ATX sources, and virtually all modern consumer computer sources are ATX sources.

How to manually check the computer source with a multimeter

How to manually check the computer source with a multimeter

1. Know the safety rules when fixing a computer to understand the dangers associated with the process. Manual testing of computer power including working with high voltage.

Important note : Do not skip this step! Safety must be a top concern during computer testing and there are a few points to keep in mind before starting this process.

2. Open the computer case. In short, this involves shutting down the computer, unplugging the power cable, and everything else connected outside the computer.

To make it easier to check the power of your computer, you should also move the disconnected and open case to an easy place to work, such as on a table or a flat surface.

3. Unplug the power connectors from each internal device.

Tip : An easy way to confirm that every power connector has been unplugged is to work with the power cable bundle that comes from the PC power supply inside the PC. Each wire group will be connected to one or more power connectors.

Note : There is no need to unplug the power from the computer as well as disconnect any data cables or other cables that do not originate from the source.

4. Group all electrical cables and connectors together for easy checking.

When arranging the power cables, you should pull them as far away from the computer case as possible. This will make checking the computer's power connections as easy as possible.

5. Short-circuit battery 15 and 16 on the 24-pin board power connector with a small steel / electrical wire. (You will probably need to look through the ATX 24 pin 12V power scheme to determine the location of these two batteries.)

6. Confirm that the mains voltage switch is set to the correct national level. In Vietnam, the voltage should be set to 120V / 220V.

Confirm that the mains voltage switch is set to the correct national level

7. Plug the PSU into a live outlet and flip the switch on the back of the power source. Assuming that the source is operating at a minimum and you have short-circuited the batteries correctly in step 5, you will see the fan start running.

Important note : Fan operation does not mean the device is supplying power to the device. You will need to continue testing to confirm that.

Some sources do not have a switch on the back. If the PSU you are testing is of this type, the fan will start running immediately after plugging the device into a wall outlet.

8. Turn on the multimeter and set to VDC (Volts DC) setting .

9. First, check the 24 pin motherboard power connector:

Connect the negative end on the multimeter (black) to any grounded battery and connect the positive end (red) to the first power line you want to check. 24 pin main power connector with +3.3 VDC, +5 VDC, -5 VDC (optional), +12 VDC and -12 VDC on multiple batteries.

You should check every pin on the connector to confirm that each line is supplying the right voltage.

10. Record the number that the multimeter displays for each tested voltage and confirm that the reported voltage is within the allowed tolerance.

Record the number that the multimeter displays

If there is any voltage other than the tolerance, replace the power source. If all voltages are within the tolerance, then your power source is not faulty.

Important note : If your power source passes the test, you should still continue to confirm that it can work well under load. If you do not want to test the PSU any further, go to step 15.

11. Turn off the switch on the back of the power source and unplug it.

12. Reconnect all internal devices to the power source. Also, do not forget to unplug the wires at 2 pin 15 and 16 in step 5 to eliminate the short circuit, before plugging back into the 24 pin motherboard power connector.

Note : The biggest mistake that occurs at this point is to forget to plug everything back in. In addition to the main power connector on the motherboard, do not forget to supply the power (s), optical drive and floppy drive (s). Some motherboards require a 4, 6 or 8 pin power connector and some video cards also need dedicated power.

13. Plug in the power, turn the switch on the back if available, then turn on the computer as usual with the power button on the front of the PC.

Note : You will run your computer when the case is removed, this is completely safe, as long as you are careful.

14. Repeat steps 9 and 10, checking and recording the voltages for other power connectors such as the 4-pin peripheral power connector, the 15-pin SATA power connector and the 4-pin floppy power connector.

Just like with the 24-pin motherboard power connector, if any voltage goes far beyond what is allowed, you should replace the power supply.

15. After the test is complete, turn off and unplug the PC, then reinstall the case cover.

Whether your power supply has proven to be very good or you have replaced it, you can now turn your computer back on and / or continue troubleshooting your problem.