the circuit board design on those old sequential circuits keyboards was pretty nuts. Like they used mabtra patterns and stuff. crazy.

anyway
here is a link to the schematics
http://www.hylander.us/images/schema...schematics.pdf

the operations manual
http://www.hylander.us/images/schema...ion-manual.pdf

there are several places online that sell the technical manual which will give you maintenance and part replacement instructions, plus there are many places you can get spare parts from

http://www.winecountrysequential.com/page6.html

these people supply survival kits and parts

I had a prophet 5 years ago
And the maintenance was challenging.

Good Luck!!