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. If the meter shows irrelevant values to the above two conditions, then the diode is defective.Hence the meter should read OL (which is equivalent to open circuit) if the diode is healthy. This is the reverse biased condition of the diode where no current flows through it. Now reverse the terminals of the meter that means connect the red probe to cathode and black to anode.For germanium diodes this value is in between 0.25 to 0.3. If the displayed voltage value is in between 0.6 to 0.7 (since it is silicon diode) then the diode is healthy and perfect. Observe the reading on the meter display.In this mode multimeter is capable to supply a current of 2mA approximately between the test leads. Keep the digital multimeter (DMM) in diode checking mode by rotating the central knob to the place where the diode symbol is indicated.Identify the diode terminals (anode and cathode).Diode Mode Testing Step by Step Instructions:
The diode testing using a digital multimeter (DMM) can be carried in two ways as there are two modes available in DMM to check the diodes such as diode mode and ohmmeter mode. Testing of a Diode using Digital Multimeter
If the meter indicates a low resistance value, then it says that the diode is healthy.Connect the positive terminal of the diode to the positive terminal of the multimeter.
Connect the negative terminal of the diode to the negative terminal of the multimeter.