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For the next test we will reverse the polarity of the meter clips as shown in Figure 9C. The red
positive (
+
) lead now attaches to the center DC output terminal and the black negative (
-
) lead
attaches to the upper diode. Do not change your meter settings; they remain the same for
both tests as shown in Figures 9B and 9D.
Figure 9C
Figure 9D
This diode as tested in this direction of polarity is good. This meter displays a value of “3.000”
flashing
indicating that the diode is blocking all current flow as a serviceable diode should.
Other meters may display “OL”.
Next, test the lower diode in the same manner as you tested the upper diode. The center DC
output terminal is common to both tests and the meter settings remain the same. The same
conditions for shorted and open diodes described in the first test still apply.
Service tips:
A continuity light is a very good alternative test device to test a diode. It has a light bulb, a
battery, a needle-like probe on the body, and a short wire lead with an alligator clip on it. If you
do not feel confident when using a digital meter, a continuity light is the preferred device to test
diodes due to its simplicity.
If your meter does not have a diode check setting, the resistance (ohms) setting may be used.
Do so ONLY if you are familiar with the meter -- false readings are common by inexperienced
users. The meter shown will indicate a good diode to have failed ‘open’ if the range is set
incorrectly (too low). Always confirm that you have good connections at the checkpoints, and
always repeat your tests.
