How to identify transistor using DMM for NPN and PNP? Simple tips for transistor checking

If you are not sure whether the transistor is NPN or PNP then just take a DMM and the transistor and follow these steps to identify transistor using DMM for NPN or PNP. You can also check the transistor for its go, no-go conditions.

1. Take a DMM and put it in Ohmmeter range. Generally the DMM has one range with symbol of a “diode” as shown below.

2. Now take the transistor. Right now we don’t know whether it is NPN or PNP.
3. Connect the red probe of DMM to middle terminal of transistor – generally this middle terminal of the transistor is base, excluding high frequency transistors like BF 594, BF 595, etc.
4. Keeping the red probe to the middle terminal of transistor, connect black probe of DMM to remaining two terminals i.e. collector and then emitter.
5. Now if you get some reading like 754Ω or something like that, but not zero*, then the transistor under test is NPN.
6. But this testing is not complete yet. Read the following.
7. Now its confirmed that the transistor is NPN. Now we shall check whether it is OK or faulty.
8. For that connect black probe to middle terminal of transistor (i.e. base) and connect red probe to the remaining two terminals i.e. collector and emitter.
9. If you DO NOT get any reading and the display shows 1— or something like that then the transistor is OK.
10. But if you get some reading in this case then the transistor is Faulty.

* You should not get reading of the DMM as zero in this case. If you get zero reading in point number 5 above, then the transistor is short-circuited from inside, and it is useless.

Now to identify the PNP transistor, use the following steps.

1. Take the transistor and connect the black probe of DMM to middle terminal of transistor.
2. Then connect red probe of DMM to remaining two terminals i.e. collector and then emitter.
3. If you get some reading like 754Ω or something like that, but not zero*, then the transistor under test is PNP.
4. Now we shall check whether it is OK or faulty.
5. For that connect red probe to middle terminal of transistor (i.e. base) and connect black probe to the remaining two terminals i.e. collector and emitter.
6. If you DO NOT get any reading and the display shows 1— or something like that then the transistor is OK, otherwise it is faulty.

* You should not get reading of the DMM as zero in this case. If you get zero reading in point number 3 above, then the transistor is short-circuited from inside, and it is useless.

Isn’t it simple enough…? 🙂