How to Use a Multimeter Tester on a Motherboard
A computer's motherboard is a complex circuit board, and you can test it with a multimeter tool to get some information about its functionality. Multimeters measure voltage, amperage and ohms with the corresponding symbols: V, A and Ω. The voltage measurement can tell you if there is power running to your motherboard and ensure that it is the right amount of power. The ohms measurement can tell you if a circuit is whole or broken. This is especially helpful when testing fuses and wires.
Perform a visual inspection of the motherboard. Look for any black or brown marks on the printed circuit board or any of the components attached to it. Examine the capacitors for any discoloration. If a capacitor has been damaged, it will show signs of corrosion or leakage that will turn the silver top a shade of brown. Often a cross shape on the top of the capacitor is the first to show the brown color. Identify any fuses on the motherboard.
Set your multimeter to measure resistance, or ohms, and set it to the most sensitive reading. Touch one probe to the one end of the fuse and the other probe to the other end. If the multimeter registers zero or near zero resistance, then the fuse if working normally. If the resistance is infinite, then the fuse is blown and must be replaced. Digital multimeters often display infinite resistance as a number "1" all the way to the left side of the display.
Test the resistance of components on the motherboard, especially if they visually appear damaged. Test capacitors by touching one probe to one leg and the other probe to the other leg. Capacitors should have a very low resistance, less than one-tenth of an ohm. If the resistance is greater than that, the capacitor is defective and must be replaced.
Measure any resistors that appear damaged. The resistance measurement is determined by the color of the bands on the resistor. Starting from the silver or gold band, the next two colored bands give the base of the resistor. From zero to nine the colors increase in value in this order: black, brown, red, orange, yellow, green, blue, violet, gray and white. The next band is the multiplier applied to the base number. Black is one, brown is 10, red is 100, orange is 1,000, yellow is 10,000, green is 100,000 and blue is one million. So a resistor with the bands silver, black, red and orange has a resistance of "0" "2" multiplied by "1000," or 2000Ω. If the resistors measurements are not in line with their banding, then they are defective and must be replaced.
Tips & Warnings
- Many multimeters have a sound option that generates a tone when the resistance is at or near zero ohms. This is helpful for quickly testing several points without having to look at the multimeter.
- Components like the processor and RAM are too complex to be tested by a multimeter.
- Often the power supply can cause problems that appear to generate from the motherboard. Test the power supply before testing the motherboard.
- Perform all of theses tests with the computer powered off and unplugged.