Yamaha CS80

Hello,
my CS-80   has the following defect:
the notes    C#   D    D#     and  G     G#    A  do not respond to AT,  in all of the octaves. All the others do. 
Thinking this to be a problem of TKC, I replaced all of the (socketed) ICs, resoldered  all of the wires, but nothing. 
The problem is shown in both CH I  and II presets.

Could somebody help me, please?  Does the AT of these two groups of adjacent keys correspond to specific component(s) / boards?

I did not check the TSBs.  Could they be involved?

Every help is very welcome.  

Ciao a tutti

Fernando 


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