On Sat, 7 Jun 2008 18:53:35 +0200, Stephan Grossklass
wrote:

Sounds like a mechanical encoder with contact problems. These things
generally aren't extremely reliable (in a set in this league, I would
have expected an optical encoder). Usually they can be unsoldered, taken
apart and cleaned with some tuner cleaner.

Determining whether it's a mechanical or optical encoder is a bit
beyond my technical capacity, but I could take the knob/wheel off and
take some pictures for you to look at if you'd be interested.