If the meter indicates a very high resistance or OL in both forward and reverse-biased conditions, then the diode is said to be opened. Since in reverse biased condition diode offers a very high resistance.įrom the above it is clear that for proper working of the diode, DMM should read a very low resistance in the forward-biased condition and a very high resistance or OL in reverse-biased condition. If the meter shows a very high resistance value or OL on meter display, then the diode is good and functions properly.Keep the selector in high resistance mode (may be 100K ohm) for the reverse bias testing procedure.Now reverse the terminals of the multimeter such that anode is connected to black probe and cathode to red probe.If the meter displays a moderately low value on the meter display, which may be a few tens to few hundred ohms, then the diode is good and healthy.When the diode is forward-biased, the resistance of the diode is so small. Connect the red probe to the anode and black probe to the cathode.Keep the selector in low resistance (may be 1K ohm) mode for forward-bias. Keep the digital multimeter (DMM) in resistance or ohmmeter mode by rotating the central knob or selector to the place where ohm symbol or resistor values are indicated.Identify the terminals anode and cathode of the diode.Ohmmeter Mode Testing Step by Step Instructions: Therefore, the multimeter will indicate zero voltage value, but in some cases it will display a very little voltage as the voltage drop across the diode. Shorted diode means diode behaves as a closed switch so the current flows through it and the voltage drop across the diode will be zero. Therefore, the meter will indicate OL in both reverse and forward-biased conditions. Open diode means diode behaves as an open switch in both reverse and forward-biased conditions. The diode defect can be either open or short.
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