# How to Use a Multimeter on a Circuit Board

Written by doug hewitt
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Multimeters can be valuable troubleshooting tools when working with circuit boards. Even if you don't have an electrical schematic of the circuit board, which would identify components and give you the voltage and resistor values that should be present, many circuit boards have test points that are clearly labelled. Use a multimeter on these test points to see if the voltage measured matches the labelled test point voltage. If they are the same, it will give you confidence that the circuit board is operating normally.

Skill level:
Moderately Easy

### Things you need

• Multimeter Probes
• Circuit Board Schematic
• Pen

## Instructions

1. 1

Plug in your multimeter probes to your multimeter, making sure you observe the correct polarity. The red multimeter probe is the positive probe and has a banana jack at the end of the probe wire. Plug the banana jack into the red multimeter plug. Insert the black probe banana jack into the black multimeter plug.

2. 2

Select your multimeter function to measure voltage or resistance by turning the function knob or selecting a function button. If you're going to measure voltage, such as measuring the power that is supplied to the circuit board, select either an alternating current (AC) or direct current (DC) voltage. The electrical schematic of the circuit board will tell you which type of voltage is present.

3. 3

Unplug the electrical device that the circuit board is a part of. Remove any housing on the device in order to gain access to the circuit board. Using caution not to touch any of the electrical components or wiring, plug the electrical device in and turn it on.

4. 4

Touch the multimeter probes to the circuit board test points if you're measuring voltage. Keep your hands on the plastic potion of the probes so you don't get shocked. The red probe goes to the test point and the black probe goes to ground or common. If you're measuring the resistance of resistors, connect one probe to each end of the resistor.

5. 5

Read the multimeter display for the voltage or resistance measurement.

6. 6

After determining the voltage or resistance, remove the probes and write down the value. Move on to the next test point or resistor and repeat the measurement. After you've made all your measurements, turn off the electrical device and the multimeter. Remove the power from the electrical device and put the housing back on.

#### Tips and warnings

• When troubleshooting electronic assemblies, keep a small bowl nearby for loose parts so you don't lose them.
• There can be dangerous voltages on circuit boards. Use caution when handling electronic devices as the voltages can cause shock and injury.

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