How to Check a Transistor With a Multimeter

How to Check a Transistor With a Multimeter thumbnail
You can test transistors with a multimeter.

Transistors are delicate and often break, but if you have a multimeter, there are some simple tests you can perform to see if they are working properly. By conducting a few quick checks with the ohmmeter function of the multimeter, you can detect almost all defects caused by rough handling. You can also perform a simple breadboard test to see if the transistor will function correctly as a switch. With many multimeters, you can also verify the gain to ensure that the transistor will function correctly as an amplifier.

Things You'll Need

  • Multimeter
  • Breadboard
  • Wire
  • Resistors
  • Switch
  • Battery
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    • 1

      Perform the six basic checks to see if the transistor has been physically damaged. Check the resistance between the base and emitter, in both directions. It should be less than 100 ohms in one direction and more than a thousand ohms in the other direction. Perform the same two tests and look for the same results between the base and the collector. Finally, check the resistance in both directions between the emitter and the collector; these two tests should show that the resistances are both greater than a thousand ohms. If you do not get these results, the transistor has been damaged.

    • 2

      Construct a simple breadboard test circuit to see if the transistor will work as a switch. Wire one terminal of a 9 volt battery to a juncture of two parallel circuits. One path goes to a switch, then to a 10k ohm resistor and finally to the transistor base. The other path goes to a 400 ohm resistor, then to the multimeter set to measure amps and finally to the collector of the transistor. The emitter of the transistor goes to the other terminal of the battery. When you turn on the switch, the ammeter should increase; when you turn the switch off, the ammeter should decrease.

    • 3

      Test to see if the transistor will work as an amplifier by using the "transistor test" mode on your multimeter. Follow the manufacturer's instructions. This test will show you the gain when the transistor is used as an amplifier. Old multimeters might not have this function.

Tips & Warnings

  • Wire up the entire circuit for the breadboard switch test before introducing the transistor into the circuit. It is also a good idea to check the 10k resistor to make sure it is somewhere near 10k ohms. High voltages can damage transistors.

  • Always adjust the multimeter to zero when you use it as an ohmmeter or change the control knob. Hold the leads together with your left hand and turn the zero adjust knob until the meter reads zero. If there is no zero adjust knob, the zero adjustment is automatic, so you do not have to worry about it.

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  • Photo Credit Hemera Technologies/ Images

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