Dear all, swapping the diode D6 did it; everything works fine. Thanks to all of you who helped, without you I would have been clueless!
Things that I fixed:
- disconnected legs 3 and 4 of IC5 (op-amp) that were connected during a previous faulty fix by someone; this restored the -15V supply.
- Replaced R195 in the power supply section for good measure, as its resistance was too low and might have blown something.
- Replaced transistor 2SC1624Y with a 2SD726 as the former measured 'closed'
- Replaced Zener diode D6 to restore +15V supply
Thanks again, everyone!
Things that I fixed:
- disconnected legs 3 and 4 of IC5 (op-amp) that were connected during a previous faulty fix by someone; this restored the -15V supply.
- Replaced R195 in the power supply section for good measure, as its resistance was too low and might have blown something.
- Replaced transistor 2SC1624Y with a 2SD726 as the former measured 'closed'
- Replaced Zener diode D6 to restore +15V supply
Thanks again, everyone!