Patches and discussion for Ensoniq VFX family

My VFX has started to detune itself. No MIDI-connections or anything i
can think of that could work as a source for the detuning. Sometimes its
small amounts and sometimes up to a full semitone. Very puzzling. A
quick powercycling usually have no effect but an extended wait before
turning it on seems to have some effect. Could it be a heatproblem?
Fixable or is it a trip to the repairman?

Regards TMB