By Douglas Quaid, Updated Mar 24, 2022
A diode is a bipolar semiconductor that permits current to flow in only one direction. The positively‑biased terminal is the anode, while the negatively‑biased terminal is the cathode. Exceeding its voltage or current limits can damage a diode, and a failed component often conducts in both directions. A multimeter provides a quick way to verify a diode’s integrity.
Attach the probes to the appropriate jacks: red to the VDC or 1 Ω slot, black to COM.
Set the dial to the “diode” mode, indicated by a triangle pointing at a line.
Identify the cathode (usually marked by a colored band) and the anode.
With the red probe on the anode and black on the cathode, the meter should display a forward‑bias voltage (typically 0.6–0.7 V for silicon). Any reading or “OL” (out of range) indicates a mis‑connection or a bad diode.
Swap the probes (red on cathode, black on anode). The meter should read “OL” or “—”. A voltage reading here means the diode is damaged.
Connect the red probe to the positive terminal and the black probe to COM.
Rotate the dial to a low‑resistance setting (e.g., 10 Ω).
Place the black probe on the anode and the red probe on the cathode. A working diode will show a low resistance (needle deflects). If the needle stays at zero resistance or indicates max resistance, the diode may be reversed or failed.
Reverse the probes (red on anode, black on cathode). The needle should remain at zero resistance. Any movement indicates a defective diode.
Always test diodes on a de‑energized circuit and consider measuring forward voltage or reverse leakage on a digital meter for a more precise assessment.
