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How to identify a defective rectifier diode - Computers & Internet

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Before you throw out that 'defective' diode, consider that your multitester may not be strong enough to truly detect current flow. Try hooking up a 9 volt battery in series with the diode (on your test bench). If the diode is good, your multimeter will detect higher voltage one way through the diode than the other way when probes are reversed. This might save you some anguish when you test a rectifier diode from a microwave, for example.

Posted on Oct 07, 2014

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You can check a rectifier diode using a multimeter - Set the meter to the lowest ohm range and place the probes at each end of the diode. Take a reading then reverse the probes at the ends of the diode and take a reading again.
A good diode will show a low reading when the diode conducts and a high reading when it does not conduct when the probes are swapped around.
A bad diode will show a low reading (short circuit) when it the measurements are taken both ways.
A bad diode will show a high reading (open circuit) when it the measurements are taken both ways.

This is may not be accurate if the diodes are still soldered to the circuit board, you may need to unsolder one leg of the diode free of the circuit board and then carry out the measurements to get a true reading on the diodes.

Posted on Mar 23, 2011


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