Yamaha CS80

There's anothe rproblem on my CS-80:

The sound is sometimes completely fading out.
This happens without detuning, so I guess it's not a supply voltage thing.
It also happens without any distortion, and its a very smooth fading.
My prime suspect is the Expression circuit: I guess the LDRs can turn an 
intermittent contact on the CV side into such a smooth fade.
I'll look into this when I'm finished tuning (i. e., not so soon), but I 
thought I mention it now; maybe one of you had a similar problem and has a 
hint where else to look.

JH.