beginner's question more infos

[Gronda Andrea]

Thanks very much for all responses, I try to put some further infos
hopening this makes the matter more clear.
The synth it's a Yamaha CS-15 .
The problem: the EG1 doesn't work.
I've got schematics.

I naively thought to check if the signal was passing through the ICs
(and other interested components) following schematic's signal path,
when I hit a key...

What I should check:  four  4558, one FET, six transistors,seven diodes.

4558 pinout
            ______
OUT A -|1    8|- +Vs
   -IN A -|2    7|- OUT B
  +IN A -|3    6|- -IN B
    -Vs   -|4    5|- +IN B
                ------