Troubleshooting the EGs
2011-11-19 by b3groover
Hi friends,
I received three replacement chips today for my CS-50, including two
VCAs and a VCA EG. Tonight I finished replacing the rest of the
electrolytics in the synth and decided to tackle replacing the chips.
I figured I'd start replacing the easier SIP VCAs, so I first replaced
the VCA that controls the pitch aftertouch. Yay! The pitch
aftertouch works and sounds great!
Next, I replaced the dead IC6 VCA on voice card M2. Yay, voice card
M2 works and the filter EG works, too! This is in contrast to voice
card M3, which I thought was the fully working card but then realized
the filter EG isn't working. And lo, I have a duophonic synth (albeit
with one voice lacking filter EG)!
Finally, I tackled the EG chip on voice card M1. I unsoldered the old
chip carefully, installed a 16pin DIP socket, and installed the new
chip, strapping the resistor on the bottom of the PCB instead of
across the top of the chip like it was installed stock. I figured it
would be easier to swap chips that way.
But oh no! It still doesn't work! The voltages from all the pins are
the same as the chip I took out... really healthy rails, the trigger
signal coming in on pin 7. But no output on pin 3.
So... does this mean that it's not the EG chip at fault, but rather
it's companion VCA? I wish I had socketed the "new" VCAs but I don't
have any SIP sockets (and Mouser didn't have any 8pin SIP sockets
either, strangely enough). Is this a common fault with these
machines? If so, I'm hoping perhaps the VCA EG chip on voice card M4
is not actually dead either, like I thought, nor is the filter EG chip
on voice card M3, but rather their respective companion VCAs.
Thoughts?
----Jim
I received three replacement chips today for my CS-50, including two
VCAs and a VCA EG. Tonight I finished replacing the rest of the
electrolytics in the synth and decided to tackle replacing the chips.
I figured I'd start replacing the easier SIP VCAs, so I first replaced
the VCA that controls the pitch aftertouch. Yay! The pitch
aftertouch works and sounds great!
Next, I replaced the dead IC6 VCA on voice card M2. Yay, voice card
M2 works and the filter EG works, too! This is in contrast to voice
card M3, which I thought was the fully working card but then realized
the filter EG isn't working. And lo, I have a duophonic synth (albeit
with one voice lacking filter EG)!
Finally, I tackled the EG chip on voice card M1. I unsoldered the old
chip carefully, installed a 16pin DIP socket, and installed the new
chip, strapping the resistor on the bottom of the PCB instead of
across the top of the chip like it was installed stock. I figured it
would be easier to swap chips that way.
But oh no! It still doesn't work! The voltages from all the pins are
the same as the chip I took out... really healthy rails, the trigger
signal coming in on pin 7. But no output on pin 3.
So... does this mean that it's not the EG chip at fault, but rather
it's companion VCA? I wish I had socketed the "new" VCAs but I don't
have any SIP sockets (and Mouser didn't have any 8pin SIP sockets
either, strangely enough). Is this a common fault with these
machines? If so, I'm hoping perhaps the VCA EG chip on voice card M4
is not actually dead either, like I thought, nor is the filter EG chip
on voice card M3, but rather their respective companion VCAs.
Thoughts?
----Jim