Archive of the former Yahoo!Groups mailing list: Yamaha CS80

Hello all. I just got a CS60 in the shop and at first it seemed easy...two of the pots (VCF/VCA Sub-osc) seem to have been shattered internally and were just hanging loose and shorting against the 15V rail. Rebuilt the power supply and kept the wires from shorting anything. The synth played fine during this, it was just always modulating. After changing the pots, I turned it on and after the first few notes it seemed all six voices suddenly died AT THE SAME TIME.

After careful testing I found that I could get the sine wave to play quietly on voice 1 and 2, and full volume on 3. I could barely hear some VCO sounds on those as well. After recapping I got 1-4 playing sine but nothing else significant.

Went through the rest of the machine as well, making sure the SH board and triggering all worked properly. All was well within specs and furthered my confusion at the death of all six cards. Eventually I swapped out a voice card from a CS50 and, to my surprise, it worked perfectly fine. I did this with a few more CS50 boards I had lying around and they all started worked. Listening at high volume to the original CS60 boards sounds as if the High Pass filter is stuck on all of them to the point that the signal is almost inaudible. Is it possible that the short damaged components that worked for a while then gave up? I didn't think all the voices could get damaged at once in the same way but that seems to be what happened here.

After testing the Filter HI/HO and LI/LO the voltages are off on the original voice boards. Am I looking at replacing all the filter chips or should I go probing all the transistors to check for a fault there first? Thanks!