# How to check transistor using digital multimeter?

1. ## How to check transistor using digital multimeter?

referred on the title,please save me on this basic theory~XD

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4. ## Re: How to check transistor using digital multimeter?

To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.

5. ## Re: How to check transistor using digital multimeter?

Originally Posted by dlhylton
To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor.
That article is wrong. There is a lot of bad information on that website.

Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around.
There is a diode junction between base and emitter, and between base and collector, but there is no diode junction between collector and emitter.

6. ## Re: How to check transistor using digital multimeter?

Basically: picture in your mind 2 diodes in series, with cathode connected to cathode, or anode connected to anode (NPN vs. PNP). The common point corresponds with a (bipolar) transistor's base, the other side of the diodes corresponds to collector & emitter.

Measure accordingly (so diode test function on a multimeter is useful). A diode shouldn't conduct current in reverse direction & thus measure high resistance then, same for collector <-> emitter when base isn't connected to anything. If collector -> emitter (or vice versa) measures a low resistance, transistor is broken.

FETs are a whole different story, though...

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7. ## Re: How to check transistor using digital multimeter?

Originally Posted by dlhylton
To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.
LOL @ the fact that although the multimeter shown has a dedicated socket for testing transistors (the round blue region), the author didn't use it but instead opted for a more convoluted, less informative, and less reliable approach.

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Originally Posted by dlhylton
To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.
LOL @ the fact that although the multimeter shown has a dedicated socket for testing transistors (the round blue region), the author didn't use it but instead opted for a more convoluted, less informative, and less reliable approach.

8. ## Re: How to check transistor using digital multimeter?

To be fair, that usually serves to measure the amplification factor (hFE). A useful indicator, but doesn't tell you everything.

I'd do a 'diode test' first to decide whether the transistor still works, then use transistor test socket if I a need a number for that hFE (which -for me personally- is rare, btw).

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