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Thread: How do you test a transistor?

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    Official Lurker DanoNJ's Avatar
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    Default How do you test a transistor?

    I have a 3 ch controller that worked fine, till the other day. Now only 1 channel works. It looks like a set of 3 transistors aid in the controll. I'm wondering if I can test these in some way and repair the darn thing.-misc-006.jpg-misc-005.jpg

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    God Bless America victory402's Avatar
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    Default Re: How do you test a transistor?

    You need a meter that can test a diode. I forget how exactly. I think you may have to desolder it to test it. I hope this helps a little. try to google it, well thats what my know it all kids tell me...lol

    Vic
    Last edited by victory402; 10-19-2010 at 09:03 PM. Reason: can't spell
    RED MOUNTAIN LIGHTS

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    This space for rent. Al in Raleigh's Avatar
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    Default Re: How do you test a transistor?

    It depends on the transistor. Is it a FET, darlington, on run of the mill NPN or PNP transistor? If you post the numbers on it, I'll try to give you an idea. Without knowing which transistor it is, you won't even know the pinout.

    If it is a NPN transistor, the base (generally) will be 0.7 volts higher than the emitter when on. When it is off, it will be less or 0 volts in a lot of cases. There are several transistor circuits where that is not the case but for the most part it is correct. When the transistor is on, the collector will be less than the power source. I know that is a stupid thing to say, but depending on how the transistor is biased is what you will see on the collector. Generally, it will be about 0.2 volts above the emitter. When the transistor is off, it will be the power source level. If you remove it from the circuit and you measure with a diode tester, the base/emitter junction should show about 0.7 volts drop. The collector/emitter junction will be something other than infinity depending on the transistor and the base/collector junction will be infinity.

    Of course all of this is incorrect for FETS, darlingtons, IGBTs, etc. Without knowing which type of transistor you basically are in the dark and any measurement you take will be suspect.
    Al

    Al

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    Official Lurker aproctor's Avatar
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    Default Re: How do you test a transistor?

    Wow. That was over my head. Considering the 3 channel controller is only about 30 bucks, I'd buy a new one and forget the FETS, darlingtons, IGBTs, NPN, PNP, & collector/emitter junctions.

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    Official Lurker DanoNJ's Avatar
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    Default Re: How do you test a transistor?

    I'm way ahead of ya

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    God Bless America victory402's Avatar
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    Default Re: How do you test a transistor?

    Yea it's a wow for sure, it took me many years just to learn the basics and I still don't know what the heck I'm doing.
    RED MOUNTAIN LIGHTS

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