Terry Given sez:

BTW in that position its probably a 47V zener, clamping the peak drain
voltage.

I'd been turning over in my mind that this is indeed a zener, not simply a
"plain" rectifier. It is indeed a 47 volt zener.

Why was this diode chosen in the design? I'm familiar with the standard diode
being used to short-circuit the back-EMF from the solenoid, but I can't
figure out the purpose of a zener used in this location.

Vdd
/\
|
|
SS
SS Solenoid
SS
|
+-----+
| |
| |
BUZ72 | /---/ ZY47
FET |--+ /\ Diode
-------| |
|--+ |
| |
\ |
0.27R / |
\ |
| |
| |
/// ///

I think that should show proper in Courier or Monaco... or Paris (c:

I must add that Vdd is *reported* to be 42vdc. I was handed this board with
scribbled specs. May be higher or lower or in a parallel universe.

Thanks,
--
John English