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HOW TO TEST DIODES WITH MULTIMETER



The diode mode test can be carried out using diode test on meter and resistance test.We shall be considering first method which is diode test.
Critically identify the terminals anode and cathode of the diode.





Rotate the central knob to the place where the diode symbol is indicated. In this mode multi meter is capable to supply a current of 2mA approximately between the test leads.


Connect the red probe to the anode and black probe to the cathode. This means diode is forward-biased.

Observe the reading on meter display. 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. For germanium diodes this value is in between 0.25 to 0.3.

Now reverse the terminals of the meter that means connect the red probe to cathode and black to anode. This is the reverse biased condition of the diode where no current flows through it. Hence the meter should read OL (which is equivalent to open circuit) or very high resistance if the diode is healthy.

If the meter shows irrelevant values to the above two conditions, then the diode is defective. The diode defect can be either open or short. Open diode means diode behaves as an open switch in both reverse and forward-biased conditions. So, no current flows through the diode. Therefore, the meter will indicate OL in both reverse and forward-biased conditions.

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 multimeter will indicate zero voltage value, but in some cases it will display a very little voltage as the voltage drop across the diode.



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