How To Test A Motherboard With A Multimeter

The motherboard is a printed circuit board that houses or interconnects all the important components required for a computer or device to work.

It is the most important circuit within a computing device, with faults on it causing the whole device to stop working, or fail to perform crucial operations.

Since you’re here, I’m guessing you spilled some water on your computer, experienced power surges or fluctuations in your home, or the motherboard is simply old and you fear that it may not be working again.

You still have to diagnose whether it’s the main problem, as replacing one may be as expensive as buying a whole new computer.

In this guide you will see the complete process of how to test a motherboard with a multimeter.

Let’s get right in.

how to test a motherboard with a multimeter

Symptoms Of A Bad Motherboard

Multiple signs point to a faulty motherboard, with some more apparent and obvious than others. Some of the most common of these include

  • The computer failing to start,
  • The device showing no sign of life when plugged into a power source,
  • Constantly getting the blue screen of death (with a boot error message and sad face),
  • The computer frequently freezing,
  • Sudden and frequent CPU restarts,
  • Failure to recognize certain hardware components like the RAM,
  • Your PC dangerously overheating,
  • Beeps from the computer, or
  • A burning smell from the motherboard. 

If you experience any of these, it’s high time you ran a test on the motherboard to know if it needs to be changed or not.

Tools Required To Test A Motherboard

To test a motherboard, you will require

  • A multimeter
  • Multimeter probes
  • Screwdriver to open up your computer.

The multimeter is the best and most important tool to use to run voltage and resistance tests on a motherboard, as well as other tests on other electrical components and devices.

How To Test A Motherboard With A Multimeter

Disconnect the computer from power, set the multimeter to 200 Ohms, and detach the ATX connector from the motherboard. Place the black lead on the metal chassis of the computer and place the red lead on one PSU AC ground slot. A good motherboard produces a zero Ohm reading.

There are more resistance tests you may carry out on a motherboard to see if it is in good condition.

You may also carry out a DC voltage test on the motherboard, and all of these would be explained in detail.

The resistance test aims to identify a short or permanently open circuit within the motherboard or power connector. 

  1. Disconnect The Motherboard From Power

To test resistance within a circuit, you don’t require current running through it.

Unplug the computing device from its power source and wait for a few minutes for the current inside of the motherboard to completely drain out.

Once you have waited for about 10 minutes, move to the next step. 

  1. Set The Multimeter To The 200 Ohms Range

Resistance is measured using Ohms, so you turn the multimeter dial to read Ohms, which is represented by the Omega symbol (Ω).

The 200 Ohms range is the lowest you will find on the multimeter and also the appropriate range to get the most accurate results for our test. 

By default, the multimeter displays “O.L” when set to measure Ohms.

To test whether the multimeter probes have been set up properly, make the two multimeter leads touch each other and see whether the multimeter presents you with a zero (0) Ohms reading.

Alternatively, you may place the two leads on the metal chassis of the computer and check for a zero Ohm reading.

If you get this value, proceed to the next step. 

  1. Detach The ATX Connector From The Motherboard

The ATX connector is a component that supplies power to the motherboard through the Power Supply Unit (PSU). The PSU converts AC voltage to low-powered DC voltage for the motherboard to use.

To expose the PSU pins, you disconnect the power connector from it. You also do this carefully so you don’t damage it.

  1. Place Probes On Chassis And ATX Pins

The first resistance test you do is on the connector. You want to test all the wires that connect to the PSU and determine the amount of resistance they have. 

Firstly, place the black lead on the metal chassis of the computer and place the red lead on each of the black-colored GND wires on the connector.

These black wires are ground connectors and are expected to produce a zero Ohm reading on the multimeter. Any other value means there’s a short circuit within the power connector. 

Once you test the GND wires, you proceed to the colored wires.

Like in the previous test, place the black probe on the chassis of the computer and place the red probe on each of the colored wires.

For these colored wires, you expect resistance of at least 50 Ohms.

If you get a reading below 50 Ohms on any of the wires, then that is the culprit and the power connector needs to be changed. 

  1. Testing Resistance On PSU Pins

If all the connector wires check out, you proceed to the motherboard PSU slots.

You will need the specific ATX-20 pin chart for your motherboard to accurately run this test. The image below shows a general 20 and 24- pin chart that may apply to you.

ATX pins values

Here, we would be testing the ground connector pins labeled “COM” to see if they have any form of resistance or not. 

Place the negative probe on the metal chassis of the computer and place the red probe on each of these black slots. You expect to get a zero Ohm reading from the multimeter from each pin.

If you get any value other than zero, you have an indication that there may be a short within the PSU.

That may be why the motherboard isn’t working, so the PSU or whole board should be replaced. The colored slots are expected to have at least 50 Ohms of resistance.

Testing Voltage On A Motherboard

Another way to diagnose if the motherboard is bad is to check if the power connector supplies it with the right amount of volts.

To do this, follow these steps.

testing voltage on a motherboard
  1. Connect Device To Power Supply

You need current running through the computing device to test the voltage in its motherboard components, so you connect it to a power source. You also connect the 20-pin connector to the PSU.

  1. Set Multimeter To 20 DC Voltage Range

For accurate results, you turn the multimeter dial to the 20 DC voltage range. DC volt is represented by “V– (with three dots)” or “DCV” on the multimeter.

  1. Back Probe Connection

Since the multimeter leads are too large to squeeze into any opening to make contact with the powered-up PSU slots, you backprobe the connection with a thin needle. 

  1. Place Probes On Back Probe Needles

Now, you pay attention here. Looking at the image provided earlier, we see that ground GND pins are located at slots 3, 5, 7, 13, 15, 16, and 17.

You place your negative probe on the needle of one of these GND slots. You may alternate between these slots to test each of them.

Moving further, you then place the red probe on the needles of the slots labeled 8, 9, and 14. These slots work with different voltages and, therefore, have different results. 

  1. Evaluating Results

For Pin 8 (PG or Power-OK), you expect a power supply above 2.5V, which is the amount of volt used by the computer to start.

This value is expected to drop to zero (0) and rise back to above 2.5V when you hit the reset button. 

With Pin 9 (VSB), you expect a value above 5 volts, while with Pin 14 (PS-ON), you expect a value between 3 volts and 5 volts.

If you press the power switch, the value from Pin 14 (PS-ON) also drops to zero (0).

Any other reading from the multimeter indicates that the power connector or the PSU pin has a fault and, therefore, needs to be changed. This is what may be causing the motherboard to fail. 

When running this test, it is important to refer to the image provided above to see the color codes and placements for each of the connections.

Conclusion

Testing a motherboard with a multimeter is an intricate procedure, given that the power connector and PSU have slots with very specific purposes.

Nonetheless, following our guide puts you on the best track to diagnosing what exactly is wrong with your computer without leaving your home.

Frequently Asked Questions

How Do You Read The Voltage On A Motherboard?

You set a multimeter to the 20 DC voltage range, back probe the PSU slots, place the black probe on a GND pin, and then place the red probe on slots colored grey, green, and purple.

Will A Dead Motherboard Light Up?

Whether a motherboard lights up depends on the part that has a fault. An entirely dead motherboard will show no signs of life, while a motherboard with a bad RAM slot, for example, may still light up.

Alex Klein Author

Author

Alex Klein is an electrical engineer with more than 15 years of expertise. He is the host of the Electro University YouTube channel, which has thousands of subscribers.