Doepfer

Hello friends.

I have this a106, that I used very little in the last 8 months.

I decided now to use it (well done!)

But:
I can't hear the resonance. I know very well the ms20. but my module
is doing a very impercettible variation to the sound moving the RES knob.

Is there any trick I need to use to jumpstart the RESO ?
any trimmer to trim ?
Is anybody experimenting my same problem?
what's the white marked IC "DS20"? (is an LM13600?)

I feel I have to change that one, the only one that can be an OTA on
the board.

Thank you for your help
at