Circuit Overview:
VLSI based digital synth that was a breakthrough in voice/dollar value. 64 voice polyphony and some interesting modulation options. 76 key keyboard. S4 module has same architecture.
Service Tips:
Always verify power supply voltages if problem looks like it could remotely be power supply related. I have seen some bad solder problems and one intermittent processor reset problem that required a new board in an Alesis product.
Parts:
Advanced Musical Electronics has a lot of parts for Alesis stuff. THey only deal with techs though.
I've also seen All electronics carry displays occasionally at low prices.