Neil,
it sounds like they sent you a surface mount component. Probably what
is called an SOT23 package or similar. (SOT stands for small outline
transistor). Since I have not seen any Germanium devices in SO packages and a
silicon device has too large a voltage drop for this application, I would
guess it is a schottky diode or most likely a dual pair of schottky diodes.
With a DVM or multimeter you can work out the correct connection and, if it
is a dual schottky you have two options: You can use one of the diodes or you
can connect them in parallel to get a slightly lower forward voltage drop.
Since these are probably small signal mixer diodes I would probably start out
by connecting them in parrallel which lands up with a voltage drop in the
diode approximately 20mV less than a single diode. (You can choose the best
option by measuring the diode voltage in the camera at about EV16-17 with the
fastest lens you own and choosing the option that gives the closest to a 210
mV drop. There are probably a number of differently pinned out devices, but
if I were to make a wild guess the single terminal on one side is probably a
common terminal for the diode pair. (i.e to parrallel the two devices connect
the leads that are on the same sides of the package together.) As an even
wilder guess the common single terminal is more likely to be the anode. If
you get the device the wrong way round the camera meter wont work at all so
even if you don't know how to use a multimeter you should be able to do it by
by trial and error. If it were by some fluke, to be a Germanium transistor,
it would act just like a pair of diodes from the multimeters perspective
anyway so the testing would be the same.
Be aware if checking voltages with a brand new silver oxide battery
under low light the battery terminal voltage may be closer to 1.6V than to
1.55-1.57V which is more typical under long term use or at higher EV.
Although Olympus claimed the diode has no effect on accuracy you can
check yourself with a multimeter and watch the diode voltage change from
approximately 200mV at EV17 down to approximately 100mV or less at EV3
(depends on diode leakage and temperature). As pointed out previously this
can easily introduce an error of from 0.3-0.6EV and even more over
temperature. I have done a bit more testing on this and am going to post a
longer discussion on this.
I hope this extrapolation from your limited info is helpful.
Tim Hughes
HI100@xxxxxxx
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