Is there a way to discover the pinout for unknown transistors with a multimeter? Without damaging them? Even if you don't know whether it's a jfet or pnp, etc? This one is a Telefunken OC603 with a dot next to one of the legs. Sometimes you can find a datasheet on obsolete xistors but usually not and it can get frustrating as my search engine skills seem to have declined recently. Thank you for your time.
Often, yes, if you're careful, and the part isn't too exotic (e.g. a low-voltage UHF transistor which blows its zap if you look at it cross-eyed). Using good anti-static precautions is recommended!
The usual starting point is to check the pin-to-pin forward voltage with a DVM or other meter which puts a current-limited voltage of no more than, say, 2-3 volts across the pins. You can figure out the direction of conduction of the B-E and B-C diodes - they'll read open in one direction, and a few tenths of a volt in the other (around .3 for a germanium and .6-.7 for a silicon). E-C will measure as open in both directions. If B-E and B-C conduct with the meter's positive-voltage pin on the base, then it's an NPN; if the negative-voltage pin it's a PNP. If I recall correctly, the B-E junction usually reads out as having a few millivolts more in voltage drop than the B-C junction - you can use this to distinguish E from C.
FETs are a different deal. A JFET will look like a diode from the gate to either the source or drain (again, about .7 volts drop in one direction and open in the other), but will conduct a few milliamps from source to drain even with the gate open.
MOSFETs read "open" from the gate at all times, if they haven't been blown by excessive voltage on the gate (e.g. static - be careful with 'em). They may or may not conduct from source to drain if the gate is shorted to the source - that'll depend on whether they're designed for enhancement mode or depletion mode.
Germanium PNP, low power (50 milliwatts), 20 volts, 50 mA, h(fe) of 50 or so, according to the documentation at
You can probably figure out the pinout pretty easily.
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arrya deefmon schrieb:
At those vintage germanium transistors center pin is the base and the collector is marked with a red dot.
Regards, Dieter
Thank you.
On Mon, 27 Feb 2006 03:44:48 GMT, arrya deefmon put finger to keyboard and composed:
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