Yamaha SK-20 -1980    Weight = 34 Lbs. Number mfg.= ? MRP=$1395

User Manual: Yamaha
Reset Proceedures: N/A
Operating System code:
MIDI or other control protocol:
Software related Links: N/A
Patches or knob settings:
Circuit Overview: below
Scematics/Service Manual:
Common Service Issues/Tips: below
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used: IG00151 VCA, IG00156 VCF, IG00159 EG, IG02600 VCA, IG03280 sustain time conv., IG03290 BBD driver, MN3009 BBD, YM63300 Trem/ens clock gen., YM62100 key assigner, YM70200 Wave gen. (Organ), YM62200 Tone gen., YM70400 Wave Gen. (Polysynth), YM62700 Position/sustain converter
General Info Links: Vintage Synth Explorer

Circuit Overview:
     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.

Service Tips:
     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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