u235vu239 wrote:
How can I clean the tape monitor button? And could it be any other
button?The signal path seems to be ok, but if there's something broken,
can it be fixed?

Anything that isn't buried inside a chip *can* be fixed, and chips can
be replaced... the question is hassle and cost.

Start by working your way through the signal path to find the problem,
then decide what to do about it.

Though if you need to ask, odds are you'd be better off getting someone
else to deal with it...