How to Test a Transistor with a Multimeter？

Testing transistors is an important test process to make sure your electronic circuits work well. If you find yourself troubleshooting a faulty PCB and need a quick measurement to see if a component has burnt out or you are validating a new design, testing a transistor with a multimeter can save you time and hassle. In this guide, we are going to show you everything you need to know about testing a transistor using a multimeter, from how to identify the type of transistor you have to understanding how to use your multimeter for accurate readings.

Why test transistors?

Transistors are the basic electronic components used for signal amplification, switching and current regulation, and usually the transistors installed on the PCB control and manage the flow of current. If the transistor fails, it can cause serious problems with the circuit (Know basic knowledge about PCB transistor, please enter here). Regular testing of transistors helps:

· Identify faulty transistors and prevent circuit failures.

· Detect component damage in advance to avoid wider damage.

· Ensure proper operation, especially in high-precision electronics such as sound systems or microcontrollers.

Now, let's learn how to test the PCB transistor with a multimeter！

How to Test a Transistor with a Multimeter?

Required Tools

Before you get started, you need to have the following tools ready:

· Multimeter (with diode mode or continuity test function)

· Transistors to be tested (BJT, FET or other types)

· Transistor data Manual (optional)

Steps:

Test BJT

NPN Transistor：

1. Set the multimeter to diode mode.

2. Connect the red marker to the base and the black marker to the emitter, and you can see a voltage drop (usually 0.6V to 0.7V).

3. Connect the red marker to the base and the black marker to the collector, and you can also see another voltage drop.

4. Use reverse polarity to test: Connect the red marker to the emitter and the black marker to the collector, so that the display should be open.

PNP Transistor：

1. The testing process is the opposite of NPN.

2. Connect the red marker to the emitter and the black marker to the base, and check whether there is a voltage drop (usually 0.6V to 0.7V).

3. Again, test base to collector.

4. Under reverse bias, the test emitter to the collector should have no continuity.

Test FET

MOSFET (N channel) :

1. Place the multimeter pen between the source and drain.

2. Apply a small voltage to the grid.

3. When sufficient gate voltage is applied, the MOSFET should begin to conduct.

4. If the MOSFET fails, a normal or non-on-on condition occurs when the gate voltage is applied.

The above several methods, if

· A transistor in diode mode does not display the expected voltage drop, or does not display the appropriate reverse bias behavior, it is likely to be faulty.

· BJT's base-to-emitter or base-to-collector test has no voltage drop or shows permanent conduction, and it may be damaged.

· The failure of the FET to switch on when a gate voltage is applied, or to remain switched on at all times when there is no gate voltage, indicates that the transistor may be damaged.