DIYbanter - How to check N-Channel enhancement mode transistor

"Golf" wrote in message
ups.com...
I know this is probably basic to most of you, by I don't remember
exactly how this type transistor operates, and therefore not sure how
to check if it is good. Can I do a diode check on it like a regular
npn/pnp transistor?

Unfortunately not, but you can check it for shorts. These are very high
impedance devices so there's not much a multimeter can tell you about them
in the conventional way.

I'm no FET expert but I believe these are the type which operate a bit like
a bipolar NPN transistor- they are usually 'off' and require the gate to be
more positive than the source to turn them on.

If you connect one multimeter probe to the drain and one to the source
(which probe to which will depend on how your multimeter is designed- some
supply positive to the black probe!) then touching the gate with a finger
should give a reading due to their extremely high gate impedace, but really
the best way is to build a little tester for them.

The source to ground, drain through a resistor and LED to positive, and the
gate touched by the finger should light up the LED. If it doesn't, a 10M
resistor from gate to positive should do the trick. A finger between the
positive and gate usually does the trick as well.

Dave