Vintage Synth Repair

>>does anybody know how the Envelope Generator 3 work in a Yamaha
CS-30? I'm not sure if it's working properly here. When assigning it
to the VCAs, the synth doesn't emit any sound. If I assign it to the
VCF I can notice a very little effect moving the decay stage. It seems
like it's producing a low voltage.<<

hey miguel- I have been using cs30 since 1983, so I know my way
around! I also have the schemos... eg3 is identical to eg2, except it
doesn't have the extra inverted output. 
eg1 is different. 
so if the voltage is lower from eg3, then there is something wrong,
yes. did you try sending the eg to the oscillator pitch? this should
confirm your finding in a more obvious way- you will hear pitch-bend
more easily than filter or vca changes. switch between C & E- they
should have the same effect normally, if the eg's are set the same.

the eg's have buffer amps on their outputs. 
(eg 1 & 2 have an extra stage after this to give the inverted version.) 
it's an op-amp called IC11 on eg3, & it's an IG00151. the input (from
the eg) is on pin 8 & the output is on pin 4. if you can get an
oscilloscope, you could check these points. VR11, VR12 & VR13 are
associated with this op-amp. the eg itself is IC14. the whole lot
lives between the eg2 release slider & the eg3 attack slider. 
I don't know if yamaha can still supply it but it's probably just a
regular op-amp.... in an inline package....
if it isn't that, then it could be the eg chip itself. it does sound,
though, as though yours is working but not at full voltage, so suspect
the op-amp.

hth-
duncan.