(a) bummer.
(b) bummer.
(c) YES, it looks like Q6 and Q7 are working. The big questions are now: is this the correct output voltage given that we bypassed the mystery device? Or does it add a Vdrop to lower WHITE (5) by some amount? And is the mystery device just a means to delay enabling WHITE (5) behind GREY (3)?
Q: While you've shorted the C4 positive to Q6 base, and WHITE (5) is +8.5VDC, is GREY (3) still outputing +13.3VDC?
If so, then it confirms that Q1 is correctly modeled (collector to mystery device) in my last (May 31) schematic.Nevermind, WHITE(5) won't be producing anything if GREY(3) didn't have a voltage on it since we're feeding part of that back to Q6 base. Further, if the zener D5 was disconnected then GREY(3) would be just a couple of volts below its unregulated side which would make WHITE(5) a lot higher than the predicted +8.8VDC.
(d) bummer.
(e) bummer.
(f) The dot on the left leg sure smells like it's indicating the cathode to me.
But there is zero chance that it has an LED with large Vdrop like a modern white LED. And your MM isn't measuring it properly. EDIT: I just checked if my bench meter's diode-check can measure a red LED. It can't. So you'll have to do it out-of-circuit. See "...report back the Vdrop on the left pair..." below.
Q:You said that R1 measures 1K but is it marked 2K?
If true, then that changed the current from 11mA to 22mA (based on 22V unreg. rail) but this should not be enough to kill the LED (if it exists) in the mystery device because many old optocouplers have robust LEDs that can take 40+mA continously.
I guess you can try to test Q1 out-of-circuit.
Q: Are you using one of those component testers that shows transistor type, EBC pinout, hFE, etc?
When you do remove Q1, confirm from the underside (based on the tab) exactly which pin is going to GND, zener, and mystery device upper-left leg. Datasheet:
https://www.web-bcs.com/transistor/tc/2sc/2SC857.phpIf Q1 is good, then you can remove the mystery device and test it separately by connecting:
i. upper left to 0V, lower-left to 1K to Vcc,
ii. upper right to 0V, lower-right to 10K to Vcc
iii. with your multimeter on VDC on the right pair.
iv. use 22VDC for Vcc from a lab power supply or lacking that a wall-wart/laptop power supply that can do any fixed value between 12VDC and 22VDC.
If it's a working opto coupler then connecting and disconnecting the 1K should cause the MM to go from 0V to Vcc.
Also, report back the Vdrop on the left pair when the 1K is connected.
EDIT: Also, while you have the mystery device out, confirm with your MM set to ohms, that there is very high resistance between any pin on the left side to any on the right side.
Good luck.