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Most Digital Multi-Meters (DMM's) have a diode test function the symbol looks something like this >| (picture the greater than sign as a black triangle pointing to and touching the redline).

Initially you should practice on a known good transistor, so you'll be able to tell if you have a bad one.

1) Ensure the transistor is out of circuit.

2) Set the DMM to the diode function.

3) Touch the positive (red) and negative (black) probes to any two leads on the transistor until you get a reading other than infinity.

4) Once you get a reading leave one of the probes on one of the leads (it doesn't matter which one).

5) Take the other probe and touch the third lead. If you don't get a reading other than infinity go back to step 4, this time leave the other probe on the lead it was originally on, when you got the reading other than infinity.

6) Now take the other probe and touch it to the third lead, you should get a reading other than infinity. If not, go back and repeat steps 3-6, but start with 2 different leads, until you can leave 1 lead in place and get a reading other than infinity on the other 2 leads.

7) If you kept the Positive lead in place you have an NPN transistor. If you kept the Negative lead in place you have a PNP transistor.

8) The probe you left in place denotes the Base.

9) On the probe that you swapped, the lead with the lower reading is the Collector and the lead with the higher reading is the Emitter.

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14y ago

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