how to check if a transistor has a fault?

Answer 1

there are several ways to check transistors. i have a self ranging multimeter that i bought from radio shack that has a built in transistor testing socket. costs about $30. a transistor tester is another option. lacking any of these capabilities a simple multimeter can be used for a tester.
a simple transistor has two distinct junctions from the emitter to the base and the base to the collector. i do not know whether you have a pnp or an npn type transistor. but in either case if
you connect your meter leads red to the emitter and black to base you should have a low forward bias resistance and when you reverse the leads the opposite (a higher resistance.
it should be noted not necessarily in that order because as i said i do not know what type transistor you have. do the same for the base to collector leads.
if either junction is shorted you will have virtually 0 resistance
likewise a reading of almost infinite resistance would indicate an open junction. one more thing to do is connect your leads to the emitter and the collector and reverse them as in the previous steps. keep in mind using the simple meter test is
kind of a go no go test at best because all of the transistor
junctions are not connected or biased as they would be in a circuit. as you might surmise the transistor has to be removed from the circuit if it was installed. hope this helps.

Answer 2

If it's a MOSFET, make sure the gate to source is an open circuit. They're static sensitive, so take precautions. If the gate is still good, it's most likely still a good MOSFET. Then you can check the on resistance if you really want. But you'll need to use a kelvin connection because the on resistance is very low on a power MOSFET.

For a BJT, measure the forward voltage drop of the emitter-base junction, and then the collector-base junction. They should act like a forward biased diode. If you short the emitter and the base, the collector to emitter should be able to block the rated voltage. Then you can measure the gain of the transistor. It should be at least as good as the datasheet. If it passes all these tests, I'd say it's good.

Bottom line is, if you need to be comprehensive, get a copy of the datasheet and start verifying each parameter.

Answer 3

Check for short circuits/open circuit between the terminals.Also check PCB connections,because if there is a short circuit the transistor will fail right after replacing it.

Answer 4

use an ohm meter to see if there is any opens in the transistor. is it an npn or pnp transistor. some of them have the values stamped on them so you can verify your test.

Answer 5

You can use a simple ohmmeter measure the forward and reverse conduction of the emitter-base and collector-base junctions. If one or both of them isn't acting like a diode, then the device is bad.

HTH ☺

Doug