Prepare the Diode for Testing
Make sure both diode terminals are clean and free of corrosion or contamination. If the diode is part of an electrical circuit, remove it from the circuit. If you cannot remove the diode from its circuit, disconnect one terminal of the diode from the circuit to electrically isolate the component for testing. Diodes let current flow in one direction, from anode to cathode. Manufacturers identify the cathode terminal of the diode with a contrasting color band. The anode is the opposite terminal. Current moving forward, from anode to cathode, encounters a small forward resistance. Current flowing in the opposite direction encounters high resistance. Test procedures depend upon measuring or comparing forward resistance and reverse resistance values.
Multimeter With Diode Test Option
Configure the multimeter to test diodes. Identify the polarity of the test probes or leads. The red lead is positive for most multimeters, but some differ. Refer to the multimeter’s manufacturer instructions. If the test indicates good results in both directions then the diode is good. Other results may indicate the diode is defective.
Ohmmeter or Continuity Setting
Configure the multimeter for resistor or continuity testing. An ohmmeter will measure very high resistance or an open circuit in one direction, and very low resistance in the opposite direction. A typical measurement for a working diode, for example, is a ratio of 10-to-1, with reverse resistance being 10 times or more greater than forward resistance. The exact measurement depends on the type of diode you are testing, its voltage rating and manufacturer. A good diode displays continuity in one direction only. A defective diode displays continuity in both directions or open circuit in both directions. Writer Bio
