arrya deefmon said:
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?
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.
This one is a Telefunken OC603 with a dot next to
one of the legs.
Germanium PNP, low power (50 milliwatts), 20 volts, 50 mA, h(fe) of 50
or so, according to the documentation at
www.datasheetarchive.com
a site which I've found to be extremely valuable in such hunts!
You can probably figure out the pinout pretty easily.
