Jonathan,
Duplicating the logic is easy. The big pain is the voltage. The Yamaha uses 4000-series CMOS and runs all the digital logic at +8.5 / -6.5 -> 15 volt supply. It’s offset above/below zero to interface with the analog circuits that run off +/- 15 volt. No modern chips run at this high voltage. Even 5-volt is history and 3.3-volt is only kept around for interfacing with older parts. All the chip guts these days are running around 1-volt. So, you end up needing tons of level-shifting chips to connect the Ardiuno (or FPGA) to the rest of the logic. Most circuits I’ve seen use chips that were intended for converting RS-232 (also fairly extinct) like the MAX232. The chips that were most commonly used won’t work anymore since they convert to +5v TTL.
David
On Jan 16, 2018, at 9:39 AM, jonathan4051@... [yamahacs80] <yamahacs80@yahoogroups.com> wrote:
Has anyone ever looked into modern alternatives for these fragile and rare 40-year old chips? I am wondering if it'd be possible to program an Arduino to handle key coding/assigning and D/A conversion on the KAS and KBC boards.Cheers,
Jonathan