I've fixed the fader problem. Actually it was a configuration problem. It was as 'pickup'. Changed into 'motor' and the problem dissapeared.
However, rotaries' problem is still there. I've noticed that if I push up or down a problematic encoder and then tweak it, is more or less working. Also if I tweak them veeeeery very slowly they also work in a normal way. But when turning in an 'accelerated mode' it does not work. Resolution in these rotaries was configured to 96.
The technician told me the machine was not usable but, as I was afraid, he didn't know too much the BCF2000.
Now I will configure it as a mackie control xt script within ableton and see how it behaves.
Any ideas about rotaries?
Btw, I'm not able to disassemble the rotaries completely. Any advice about how to do it clearly?
Thank you all, really!