[sdiy] A part for a CS20M

[John Henson]

Thanks for the replies,
Steve's explanation summed it up very well, and it does run on +5V and 
-10V. It would take quite a bit of CMOS logic to achieve this function.
Interestingly enough, the memory preset LED section is one part of the 
synth where using the YM617 is unnecessary, and Yamaha used a lot of 
extra circuitry to turn the outputs of the 617 into something to drive 
LED's. Ironically this is a cosmetic issue, the switches function 
correctly and call up presets as expected. If any other YM617 had 
failed, the synth would be unusable (lucky escape for the client).
I got the CS20M service manual quite easily on-line, maybe it was from 
manuals.fdiskc.com/flat  there is no clue from the manual itself.
Regards,
John.