How to Check a Diode
- 1). Place the multimeter on the diode setting. This is usually indicated by a small diode symbol on the casing.
- 2). Measure the forward-biased voltage on the silicon diode. Do this by putting the positive or red lead on the anode side of the diode, which is unmarked. Place the negative or black lead on the cathode side of the diode, which is marked by a stripe.
- 3). Record the voltage. An undamaged silicon diode will read 0.5 to 0.7 V when it is forward-biased.
- 4). Measure the reverse-biased voltage on the diode by switching the multimeter probes. Place the positive or red lead on the marked or cathode side of the diode. Place the negative or black lead on the unmarked or anode side of the diode. You should get a reading indicating infinite resistance or no current flow.
- 5). Repeat steps 1 to 4 for the germanium diode. An undamaged germanium diode will typically read 0.1 to 0.3 V when it is forward-biased, but will also show infinite resistance when it is reverse-biased.