Morning!
I replaced R5 on the "Control Board" with a 22K resistor, and temporarily replaced the open fine voltage adjustment front panel pot with a 230 Ohm resistor.
The supply seemed to behave with full control of the voltage out at the rear terminals. I took the measurements suggested at the pins of IC1 and VT2. I also found a couple of other issues. The front panel volt meter is stuck, looks like a bearing issue. I think they are still available though. The coarse front panel pot for current is scratchy and intermittent. I will replace all the front panel pots I think! Current control worked against shorted rear terminals. Whether the thing seems to work is a result of removing the open front panel fine voltage adjustment pot i don't know, or as a result of the much higher 22K resistor in position R5 as opposed to the original 470 Ohm one.
With 7.95 V DC showing on the rear output terminals, and 5.32V AC on the main transformer secondary, these are the pin out volts relative to the +15 0 -15V supply 0 volt rail.
IC1:
Pin 1 - 15.32
Pin 2 0.0
Pin 3 0.04
Pin 4 - 15.53
Pin 5 - 15.55
Pin6 - 0.540
Pin 7 15.39
Pin 8 Not Used
VT2:
Collector 8.56V
Base 2.22V
Emitter 1.609V
The voltage output of the transformer secondary adjusted from 0.14V AC to 25.32V AC with the front panel voltage control
The rear panel output terminals voltage adjusted from 0.33V DC to 56.8V DC with the front panel voltage control
Could the problem have just been that the front panel fine voltage control was open circuit anywhere other than fully counter clockwise?
Dare I reinstate the 470 Ohm resistor at R5?
Thanks!
Oh, and the rest of the parts to build a duplicate "Supplies Board" to replace the missing one arrived, the board's fully populated now, and works fine in both power supplies
PITA about the meter, I can see one being quite dear, if available at all anywhere.
UPDATE!!I added a parallel resistor across the 22k R5, and monitored the voltages. I used another 22k at first, then reduced the resistance in three steps. All was still well, so I removed the 22K and refitted the 470 Ohm one. All still fine. Needs a new front panel fine voltage adjust pot, so I will renew all 4 pots. All I can assume is having the series connected 10 Ohm and 1K ohm front panel voltage control post go open at anything other than fully counter clockwise on the fine one, was the cause. Is this feasible? I am happy it lives again, would just like to understand why though