"g. beat spam protected wrote in message
. ..
This surface mount device is about the same size as other surface mount
diodes (1N4001, 1N4007) that I have dealt with.

Markings: PH-17D and cathode band

It appears to be a garden variety diode.
Diode test on Fluke 87: 0.587

More curious about ratings.

g. beat

Well, it appears to be a 17 volt Zener diode.
I have reverse engineered enough of this circuit (and a few voltages
measurements) -
to convince myself this is indeed a zener - probably 1/2 watt?

The circuit is Weller's original control board (circa 1980s) for the "EC"
series of soldering stations. Ceramic substrate and all surface mount (not
bad for a 20 year old board - date stamped).

Anyway, this control line is "LOW" (~ 1 volt) when the Triac is ON
(soldering iron heater ON)
and goes "HIGH" (~22 volts) when Triac is OFF (soldering iron heater OFF).

This allows the LED in-line with the 24 VAC ..

LED is ON, when control line is LOW
LED is OFF, when control line is HIGH

So, this appears to be the logic they used to create LED status light for
heater activation :-)

g. beat