12-25-2016, 10:49 AM
Ron, looking at the schematic, it appears that PL8 is part of the circuit. When a stereo signal is received, pin 6 of IC 30 is pulled to ground, lighting PL8. Transistor TR307 is an inverter, so when PL8 is on PL9 is off and vice-versa.
It looks like PL8 is the actual stereo light and PL9 is only on with a mono signal. The base drive for TR 307 is supplied through PL8 and if it is open, TR307 cannot turn on and light PL9.
Try connecting a 470 ohm resistor across the open bulb PL8 to supply base drive to TR307 and see if PL9 now lights in mono.
It looks like PL8 is the actual stereo light and PL9 is only on with a mono signal. The base drive for TR 307 is supplied through PL8 and if it is open, TR307 cannot turn on and light PL9.
Try connecting a 470 ohm resistor across the open bulb PL8 to supply base drive to TR307 and see if PL9 now lights in mono.
