The LF353 IC is a notorious troublemaker.
It can fail in many ways;
It can generate noise, clicks, bangs, hiss etc.
It can lose gain and start a DC drift
It can become intermittent or play completely dead.

It's a very cheap component and not all too difficult to replace.
I would suspect an LF353 over a trimmer that has gone out of adjustment by itself anytime.

Martin

Hi Martin!

Thanks for the explanation and sorry for the long post above - I thought that the new capacitors on the tuner board may have made some very small adjustment required, since the auto tune was working correctly before the recap. I think I'll leave the tuner like this for now (it is totally usable and sounds very good) and with no hurry investigate what the problem is by trying a new IC.

More important, I think I'll have to check again the bias of the right channel, since it's again running a bit hot...

Thanks again,

Marco