Electronics Testing

fet testing ...

To test N channel MOSFETs for basic functionality, follow these steps:

• 1: Ensure the MOSFET is out of circuit, then place the DVM into the Diode test position. Attach the positive lead (Red) to the Drain terminal, and the negative lead (Black) to the Source terminal. Confirm an Open circuit condition.
• 2: Leaving the negative lead (Black) attached to the Source Terminal, remove the positive lead (Red) and briefly attach it to the Gate terminal. This applies a voltage to the gate of the MOSFET through the DVM's internal battery.
• 3: Repeat Step 1. This time, confirm device conduction.
• 4: Attach the negative lead (Black) to the Gate Terminal, and the positive lead (Red) to the Source terminal. This turns the device off by reversing the Gating voltage (making it more negative). Repeat Step 1, and confirm an Open circuit condition.
• 5: If the MOSFET has a built in Protection Diode (this is connected across the Drain and Source Terminals), attach the negative lead (Black) to the Drain terminal, and the positive lead (Red) to the Source terminal. Confirm a forward voltage drop of between 0.2 to 0.8V DC.

For P channel MOSFETs reverse the multimeter probe polarity.

transistor testing ...

NPN transistors can be tested by using the diode test on a digital volt meter. A working transistor should test correctly between the base and collector and between the base and emitter (Negative probe on base). There should be no continuity between the collector and the emitter.
For PNP transistors reverse the multimeter probe polarity.