Quad 33 and FM3

[ppppenguin]

Power supply was OK so I put it back in the system. This time I got intermittent sound with both voume and balace controls very crackly. Using the pushbuttons gave horrible pops and bangs. First thought was DC in the pots and switches. I'd replaced the 100u caps in series with the balance control but they shouldn't affect the volume control or switches.

I'll make a few DC measurements around the controls and see if I can reason out what's happened. For now it's a bit mysterious.

I should add the all the other electrolytics (on the plug-in boards) were replaced less htan 5 years ago.