This nice little 90's amp found it's way to me with the comment ...
"Just needs a squirt of switch cleaner, one of the volume controls doesn't work"
Sadly not.... and I can see marks on the PCB where someone had been liberally spraying the stuff at the poor innocent volume control!
What happens is the joints break up between the volume pots and the PCB... leading to an intermittent or non-existent connection.
A quick solder up of these joints provides a long lasting repair.... if only it was a quick job. Most amplifiers of this design require a considerable amount of disassembly to get to the joints. Joints to and from the phono connectors on back panels present a similar problem.
Just to show you how long this sort of thing takes, here's a time-lapse video I made (and I wanted an excuse to try some sort of overhead camera thing!). This repair took an hour!
... still better than a "soundbar" or other hideous self contained speaker.