Can someone help me translate what these readings are on a transistor?

[requim]

I have a transistor that I think is bad and I have the datasheet for it (or I think it's the right one).  The results I get are 0L for everything but red on pin 3 and black on pin 2 which gives me a voltage drop of about 0.5 V.  I used a Fluke 87V on the diode setting.

I've attached a pdf of the datasheet.  What should I be expecting from a good transistor? And what do my readings mean?

Thanks!

[IanB]

It's a MOSFET and unless you turn it on it conducts only from source to drain? In other words, it seems to be behaving as the datasheet implies it should behave?

Now I'm no expert, so doubtless an EE will be along shortly to put me right.

[amspire]

I have a transistor that I think is bad and I have the datasheet for it (or I think it's the right one).  The results I get are 0L for everything but red on pin 3 and black on pin 2 which gives me a voltage drop of about 0.5 V.  I used a Fluke 87V on the diode setting.

Those results are exactly what you would expect. It is almost certainly fine.

[requim]

Bummer.  Looks like I'll have to keep searching to figure out what died on me.  It appears something shorted out since I'm getting 0L on a number of circuits on the power supply.

For clarification I took readings while it was powered on and the readings I had were:

pins 1 & 2 - 168V
pins 2 & 3 - 168V
pins 1 & 3 - 0.2V

Does that seem reasonable?

[IanB]

Pin 1 is the gate. A voltage on this pin switches on the transistor and allows current to flow between pins 2 & 3.

In a power supply the transistor is probably being used to chop up DC into pulses, so you would expect the gate voltage to be changing at some moderately high frequency. You would really need to probe the waveform at the gate to see if this looks right, but that's not easy as the circuit is on the high side of the power supply and is mains live.

[requim]

I'll re-solder it back into place and pull out the iso transformer and oscilloscope and try probing it.  With any luck I won't kill myself or my equipment.

What should I look for in the waveform, or should I just post it on youtube and put a link to it here?

edit: nevermind.. I think I know what to look for based on your statement of high frequency change..

[IanB]

I think you would be looking for a PWM waveform. The control circuitry will vary the PWM signal on that transistor to regulate the output voltage on the secondary side.