Page 63 - Testing Electronic Components

Testing Diode

When comes to testing diode, you need a special method to test it. If you
do not know how to accurately check a diode, you will not be able to
repair or troubleshoot electronic equipment because a spoilt diode you
may think that it is good and you will definitely waste your precious time.
Diode is label as “D” in circuit board. Usually a rectifier diode can fail in
one of the four ways.

It can become open circuit, short circuit, leaky and breakdown when
under full load. An analogue multimeter or digital multimeter can be used
to test or check for all the first three conditions except the last one which
is the diode breakdown in full operating voltage. Diode breakdown when

under full load means the diode test okay with your meters but failed
when a high voltage flows through it.

From my experienced in the electronic troubleshooting field, I discovered
that testing diode using an analogue multimeter is more accurate or
precise than using a digital multimeter. I could explain to you in details
why I preferred analogue meter. I do not know about you because I really
came across quite a number of diodes where it tested ok with digital
multimeter but failed when check with analogue multimeter. The first
step on how to test a diode accurately is to remove one of the diode lead.
You can't always be certain if a diode is good or bad if you perform in-
circuit test, because of back circuits (parallel connection) through other
components.

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