Sir vstyn . . . . .
With time onset . . .expect that cap C41 possibly may have declined in capacitance. YELLOW RECTANGLE . . .MARK-UP
Sub another like value unit across it to see if volume comes up.
Its rated at 100 ufd at 10VDC or greater.
Coming up . . . . . .
Do you have a VCR -CD or DVD player with their RCA audio output audio jack that will provide a working audio signal to inject into the unit with a RCA to RCA patch cord to then trace audio signal flow, within the unit ?
Now, needless to say that with this capacitor bad, the volume control will still have its affect at the low end of its adjustment spectrum, but at max volume the audio output level may have declined to a LOUD whisper.
Schematic of Units Involved Audio Area:
View attachment 28854
73's de Edd