Page 128 - Testing Electronic Components

middle pin then the middle pin is the “Collector”. If middle pin is
the collector, the third pin must be the “Emitter”. If the red probe
is on the middle pin, touching your finger between the base and the
middle pin, the pointer will not move at all! In other words, if you
test a NPN transistor, look for the black probe and if you test PNP
transistor look for the red probe. If there is no response from the
meter (pointer won’t move) even after you have use your finger to
touch on the pins, then the transistor has developed an open circuit.

Note: For checking PNP transistor, perform the same test by reversing
the test probe.

These tests also give some indication of a transistor’s condition. If the
transistor does not check out as describe above, there may be something
has gone wrong with the part. For example, if the emitter collector
junction shows a low resistance in both directions at x 10 K Ohms, the
transistor is shorted.

For many of you, this probably seems like a lot of transistor information
to absorb. Checking transistor is not as easy as checking the two leads
devices like the resistor, capacitors, diodes and etc. In reality, this is only
the surface of a fairly deep subject. Experimenting with a few
transistors and a multimeter as you go back through the material is

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