Originally Posted by
Marcel
While you have it open on the bench changing those chips you might want to de-goop the input section of the board.
I had a old VOX VT amp that had yellowish goop holding some parts in place. When new the goop is fine but with a little age and if it is in contact with components in the input stages audio path it develops a weird electronic ability which translates to all kinds of static type noises. Get rid of the goop near input stage components and the noise goes away. In the VOX it completely covered the 1M SMD resistor to ground that referenced the 1st OP amp so the noise was permanently present though far less obvious when the gain control was wound down. Unfortunately when I removed the goop the SMD resistor came off with it so that component needed to be replaced for the amp to work as intended...
The goop when old and hard has far less effect in the main audio and the power section, though it can sometimes slightly upset bias currents...