Page 127 - Testing Electronic Components

Now you must determine which lead is the “emitter”, and which is the
“collector”. Assuming you are checking an NPN type of transistor and
you already know that lead number 1 is the base, and now you must
determine which lead (lead 2 or 3) is the collector. First, set your
multimeter ohm’s range to x10kΩ. Connect the test probe according to
the diagram shown in Figure 4.

∞ ohm 0 Test Black probe Red probe is Reading in
No is connected connected to ohms
to pin no pin no
1 2 3 High (∞)
2 3 2 Low

X10kΩ
NOTE: Certain Transistor might showed high (∞)
- x1 Ω + reading on both test (either way).
+
Black probe Red probe

BASE
1 2 3

Figure 4 : Identifying the collector lead of an NPN transistor

1. Look for the high ohm reading (Test no: 1) and see which lead the
black probe is connected to.

2. From Figure 4 the black probe is connected to lead 2 and this lead
is the “Collector” and lead 3 is the “Emitter”.

3. Some transistor will show two high ohms readings and if it is the
case you should use your finger to touch on the base (first pin) and
the middle pin while you are still holding the probes on the

transistor middle and the third pin. Assuming while your finger
touching the base and the middle pin, the pointer show some
resistance then looks at the probe. If it is the black probe on the

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