Is there a simple/easy/feasible way to test JFET/MOSFET pinouts?

[Mark Hammer]

Whenever I have a Japanese bipolar transistor, or a metal-can type, or a germanium transistor, if I don't have a datahseet for that manufacturer to confirm for me what the pinout is, I simply insert the transistor into the hfe-testing socket in my meter, set it to NPN or PNP, and change the transistor's location in the socket until I get an hfe reading that is plausible.  It has helped me identify that some devices were different pinouts than I thought, and assisted me many times in finally getting a circuit working.  I always try to have datasheets on hand for the device in question, but sometimes you get house-brand equivalents, or else salvage useful transistors from scrap boards, and you have no idea who made the device.  Sometimes, you can't find a pinout anywhere.  That's when my trusty transistor-tester setting comes in VERY handy.

But what about JFETs and MOSFETs?  Is there a way to identify which pin is which, using some similarly easy technique?

[R.G.]

It's in the junctions.

Set your multimeter to low ohms, preferably the diode-test range if it has one. This will tell you which direction of a diode conducts.

1. For bipolars: Use the multimeter and find which lead conducts to which. For a good bipolar, the base is the only lead that conducts to two others when the polarity is right, no conduction at all in the reverse direction. Collector conducts to base in the correct polarity, as does the emitter, but not to each other. When the base is identified, test gain. There are now only two ways to try gain, and the collector and emitter are correct when it reads the highest gain.

2. For JFETs: Drain and source conduct to each other both directions. Gate conducts to both drain and source one direction (junction forward biased) and not at all in the reverse direction (gate reverse biased). There is a 90% chance that drain and source are interchangeable.

3. For MOSFETs. The gate never conducts to any of the other pins. The substrate diode conducts the reverse direction of the channel, so for an N-channel, the substrate diode conducts with anode to source, cathode to drain.

[frank_p]

From a link at GEO:
http://www.repairfaq.org/REPAIR/F_semitest.html

[Gus]

With a power mosfet you can sometimes watch the gate charge with the DMM set to resistance the DMM will show some resistance and then go to over range.

[R O Tiree]

Worth its weight in gold... TEH CLICKY

No messing about with DMMs - just connect any 2- or 3-leg semi-conductor any which way you please, press the test button and after about 3 seconds, you get a readout of what it is, which pin is which (except JFET D/S - ambiguous), and by continuing to scroll through the pages, you get things like hfe, Ib, Ic, Vbe, leakage current for BJTs and similar useful info on other devices under test.

Not only useful for helping to identify "house branded" items, as Mark was talking about above, but also useful for checking an item if you think you might have fried it, for example.