The ‘Distortion Harmonics’ switch would only have an effect in one(top) position and in the other two there would be almost no output. First thing was to check the switches themselves which turned out to be fine. Later I checked the quad op amps which seemed to be OK. Replacing the Switch IC solved the problem. It took a while to figure it out as I didn’t think it would be that chip but rather something around the actual mechanical switch. Everything around that was fine though so I left replacing that IC for last. I’m glad it worked!!

Old one:

New one: