SK series synths are divide down oscillators with analog filtering of the organ voicings (using mostly op amps etc.) and the classic filter of the CS series for the synth section filtering. I've finally aquired an SK-20 here which has two string presets mixable with the perc organ drawbar section and rather standard polysynth with an adsr and filter controls.
Mine appears to have lost the key assigner chip. Looking for one at the moment. They use ground and -15V for the rails on that chip and others in that section including the clock it appears.
While Yamaha normally does not keep parts around more than 5 years or so, I stock what I can. I have a scrap unit.
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