I had some documentation on circuit bending the Casio SA series up, but while helping somebody work on their own I realized how shoddy, old, and ugly those old images were and decided to make a new one. This new diagram includes all information I’m currently aware of in regards to circuit bending the Casio SA-2 (and many others in the Casio SA family) based on personal experience and available information scattered across the internet.
Over at the schematics page