Testing Diode-The Accurate Way On How to Test Semiconductor Diode Using Multimeter
To Test Diode And Other Electronic Components Like A Porfessional
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Professional In LCD Monitor Repair
Testing diodes is
different from testing a resistor because you need a skill to do it.
If you do not know or wrongly test a diode you will be unable to repair the
A bad diode you think it is good. This will definitely waste your precious
A rectifier diode can fail in one of the four ways. It can become:
-Breakdown when in full operating voltage
An analog multimeter or digital multimeter can
be used to check
for all the first three conditions except the last one where the
diode breakdown in full operating voltage. From my of experienced
in the electronic repairing line, i found that checking diode using analog
multimeter is more accurate than using a digital multimeter. I could explain
to you why i preferred analog meter. I do not know about you because i
came across quite a number of diodes where it checked ok using digital
but failed when test with analog meter.
The first step on how to test a diode 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,
of back circuits through other components. To be absolutely sure, you will
lift, or disconnect, one diode lead from the circuit to avoid back circuits.
Unless you are very sure about the board you are checking. Sometimes i do
diodes when checking it on board. Your experienced will tell you when to
check a diode
on-board or off-board. If you are new to electronic repair, i highly
you check a diode with a lead removed from the board.
I will set my analog meter to x1 ohms to check for current diode leakage
forward testing. Connecting the black probe of your meter to the cathode
and red probe
to the anode, the diode is reverse biased and should look like an open
the red probe of your meter to the cathode and black probe to the anode, the
diode is forward
biased and the meter should read some value of resistance. If you have two
most probably the diode is shorted or leaky and you should replace it. If
you don't get
any reading either forward or reverse bias, the diode is considered open.
The real problem
when checking a diode using the diode test function of a digital meter is
that an open or
leaky diode, the meter sometimes reads ok(0.6). This is due to digital meter
diode test output
voltage (which you can measure the output test probe using another meter) is
500mv to 2v. An analog meter set to x1 ohms have output about 3V(remember
the two 1.5V
battery you installed in the meter!). The 3V voltage is enough to show you the accurate
reading of a diode when under test.
Even if you have a good reading at x1 ohms doesn't mean that the diode is
good . You
now have to set your meter to x10K to test the diode again. The output
x10k ohms is about 12V(remember the 9v battery in your
the diode under test should show only one reading. This is exception to
where it have two readings but not shorted reading. If the meter showed one
the diode under test is good. If it has two readings then most probably the
diode is either
shorted or leaky. The digital meter can't test it because the output from
the meter is only
500mv to 2V.
If a diode breakdown when under full operating voltage, there is no
way to testing diode (unless you
have a very expensive diode checker which specially designed to
locate this type of problem).Substituting with a known good diode is often the only way to prove that an
is causing a particular problem. Sometimes an intermittent diode could be
locate using a coolant
Caution: Be certain that power is removed from any circuit before performing
any of the following
diode checks, otherwise meter or circuit damage could result.
Conclusion-In order to correctly test diode function you need to set
the analog meter
to x1 ohms and x10K ohms range.