How To Test A Motherboard With A Multimeter

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

Nonetheless, replacing a motherboard gets as expensive as buying a whole new personal computer, so it’s great to diagnose whether it’s the main problem in the first place.

Our article presents you with all you need to know about testing a motherboard for faults, including symptoms to watch out for, and multiple step-by-step guides on diagnosing it from the comfort of your home.

Let’s get right in.

how to test a motherboard with a multimeter

How to Tell If a Motherboard Is Bad

Multiple signs point to a faulty motherboard, some more apparent than others. While some of these are physical, other signs of a faulty motherboard come from how your computer or device may be acting. 

Some of the most common physical signs you would notice with most bad motherboards include

  • Scratches, which affect the copper traces and puts your board at risk of shorting 
  • Cracks, which are signs of massive physical damage
  • Corrosion from water damage, which affects its circuitry and only gets worse over time
  • Burn marks or burn smells coming from the motherboard, which signals that a component has blown due to a possible short in the circuit or overcurrent. 

The presence of these physical damages or some other underlying factors affects how your computer behaves. You may then notice other symptoms of a bad motherboard, such as

  • 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 restarting
  • Failure to recognize certain hardware components like the RAM
  • Your PC dangerously overheating
  • Beeps from the computer

If you experience any of these, it’s high time you run 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.
  • Back Probe Pins
  • A power source 
  • The motherboard manual
  • Safety apparel, most especially safety gloves

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

With the PC connected to power and the ATX still plugged in, set the multimeter to the 20VDC range. Connect the black lead to a back-probed black ATX wire and connect the red lead to other colored wires. A good board produces a reading close to 3.3V, 5V, or 12V, depending on the wire you test.

There is more to this test; you may also carry out a resistance/short circuit test on the motherboard. You can also test the motherboard’s capacitors, which will be explained in detail shortly. 

The voltage test allows you to check if the connector supplies the motherboard with the right amount of volts. Unlike the resistance test, this test allows you to diagnose how the motherboard behaves when used. 

To do this, follow these steps. 

  1. Connect the Device To a Power Source

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

In this first step, you need current running through the computing device to test the voltage in its motherboard components. So, you ensure the ATX is plugged into the PSU, and then you connect the device to an electricity source. You also connect the 20-pin connector to the PSU.

  1. Set the Multimeter To 20 DC Voltage Range

You turn the multimeter dial to the 20 DC voltage range for accurate results. 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 contact the powered-up PSU slots, you backprobe the connection through the cable using a thin needle. You can watch a video on how to backprobe a connection

  1. Place Probes On Back Probe Needles
ATX pins values

The 20 and  24-Pin Chart

Now, you pay attention here. The image above shows that ground GND pins are located at slots 3, 5, 7, 13, 15, 16, and 17. Using a needle, backprobe any of these slots through the black wires and place your negative probe on the needle. You may alternate between these slots to test each of them.

Moving further, you then backprobe any of the other slots and use the red probe to test them. These slots work with different voltages and, therefore, have different results. 

  1. Check for Appropriate Voltage Readings

Different colors represent the slots, and each color has a specific voltage reading to expect when you test them out. 

  • Orange (+3.3V)

There are three orange slots in a 20-pin setup and four orange slots in a 24-pin setup, and orange wires represent all of these. All the orange slots work with just over 3.3V.

  • White (-5V)

When tested, the White wire is labeled NC and produces a reading below 5V.

  • Red (+5V)

The 20-pin setup has four red slots, while the 24-pin setup has five red slots, all represented by red wires. Each of these should present a reading of just over 5V when tested. 

  • Grey (+5V)

The grey wire represents the Power_Good or PWR-OK slot, which tells you whether the computer has enough power to start. When tested with the GND pins, you expect a value above 5V. When you hit the power button, this value will drop to zero (0) and rise above 5V. 

  • Green (+5V)

The Green wire is for the PS-ON slot and shows a value of just over 5V when tested. If you press the power switch, the value from this wire also drops to zero (0).

  • Purple (+5V) 

The purple wire is for Voltage Standby and is expected to present a constant value just above 5V when tested. 

  • Blue (-12V)

There’s only one blue wire in all types of connectors, which is expected to show a voltage below 12V.

  • Yellow (+12V)

There are two yellow slots in the 24-pin setup and only one in the 20-pin setup. These pins, represented by yellow wires, are expected to produce just over 12V when tested. 

Any other value from the multimeter indicates that the power connector or the PSU has a fault that must be changed. This is what may be causing the motherboard to fail. When running this test, it is important to refer to the image above to see each connection’s color codes and placements.

Resistance/Short Circuit Test

The resistance test aims to identify a short or permanently open circuit within the motherboard or power connector. This is why it is also known as the “Short Circuit Test”

  1. Disconnect The Motherboard From Power

You don’t require current running through a circuit to test resistance. Unplug the computing device from its power source and wait a few minutes for the current inside the motherboard capacitors to drain out completely.

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

  1. Set The Multimeter To the 20 Ohms Range

Resistance is measured using Ohms, so you turn the multimeter dial to read Ohms, represented by the Omega symbol (Ω). The 20 Ohms range is the lowest you will find on the multimeter and 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 computer’s metal chassis 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

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 a Metal Surface And 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. 

  1. Check for Multimeter Ohm Readings

The black wires are ground connectors expected to produce a zero Ohm value 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 value below 50 Ohms on any of the wires, 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 20-pin chart for your motherboard to run this test accurately. The image below shows a general 20-pin and 24-pin chart that may apply to you.

ATX pins values

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

Place the negative probe on any metal surface near you and place the red probe on each of these black slots. You expect to get a zero Ohm value from the multimeter from each pin.

If you get any value other than zero, there is a short within the PSU. That may be why the motherboard isn’t working. In this case, the PSU or whole board should be replaced. 

The colored slots are expected to have at least 50 Ohms of resistance. A bad value here also signals that your motherboard PSU is faulty and needs to be replaced. 

Testing the Motherboard Capacitor With a Multimeter

Capacitors are often cylindrical components soldered onto the motherboard and used to regulate the electricity supply to other fragile components. They also store electricity to be used later when there is no active electricity supply to the motherboard.

This means they still hold an electric charge when the motherboard is unplugged from the power supply, and you are at risk of an electric shock. 

To test a capacitor, however, you must test its resistance to ensure it isn’t too low. The resistance of a capacitor is expected to be infinite (often regarded as an open connection). 

  1. Set the Multimeter to Measure Ohms

With the motherboard disconnected from any electricity supply, put the multimeter in the 200 Ohms setting.

  1. Place Probes on Capacitors’ Terminals

There are many capacitors on the motherboard, and if you look at each, you see that they have been soldered to the board at two points. Place your multimeter probes on each of these points to get your measurement.

Ensure the probes don’t contact each other to prevent any shock hazard. Remember that the capacitors hold a charge even after unplugging them from power.

  1. Check for Infinite Resistance

Finally, you check the multimeter screen and look for an infinite resistance reading. Infinite resistance is represented with “1” on the digital multimeter, and any reading other than “1” is regarded as bad. You should replace any capacitor that shows you a faulty Ohm value.  

Repairing and Replacing Your Motherboard

Motherboards can be repaired. However, fixing them can be difficult. Due to the fragility and intricacy of the components, a little damage on the board can lead to issues on multiple other components in a way you can’t predict.

Your board will only function properly when you take care of all these components, which requires a lot of skill and time.

testing voltage on a motherboard

Replacing a board is much easier, but you should also be careful here. Always ensure your replacement is a direct substitute for your old motherboard and compatible with your computer. 

Frequently Asked Questions

How Do I Know If My Motherboard Is Bad?

Apart from scratches, cracks, and burn marks, some other symptoms of a bad motherboard include your PC freezing, suddenly restarting, overheating, failing to start, and showing no sign of life.

What Is the Voltage of A Motherboard?

Although the motherboard uses a standby voltage of about 5V, the ATX connector supplies it with differing voltages of 3.3V, 5V, and 12V. The standby voltage is used to power the computer.

Alex Klein 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.