Hi Florian, thanks for adding me. 

Basically some corrosion from a leaky cap had eaten some traces on the envelope/filter board. I posted on gearslutz about it 

http://www.gearslutz.com/board/electronic-music-instruments-electronic-music-production/608707-korg-mono-poly-envelope-problem-easy-fix.html

to get some "professional" opinions. Someone mentioned this M/P group so I figured I would join. I'm pretty new to soldering/electronics stuff, but this improved my confidence and interest in maintaining and repairing (at least little stuff) synths.

best,

Paul