https://ia801500.us.archive.org/22/items/synthmanual_DC-50_service_notes/DC-50_service_notes.pdf
May be some other gems tucked away in there!
How very much things change!
A BBD-based chorus would today be advertised as "analog" and much blather based on it not having an A-D and D-A converter. In reality both techniques will have sampling noise and heterodyning. The real digital version will have quantization noise, which can be mostly digitally suppressed.
Funny.
The clock looks similar to the CE-1.
Was this the beginning of "Boss FET switching"
Change this clock to a monostable configuration for the now famous and widely repeated switching.