Eraser from CircuitBent.it was kind enough to share his bend point schematic for the Yamaha RX-17 drum machine. The points are labeled with pin number and a chip ID along with their suggested corresponding connections. More info at CircuitBent.it RX-17. Pictured below is another RX-17, recently crafted by Logan aka LameBoy from 8Bit Collective.

The controls and RCA patches are on the main PCM chip without any extra circuitry like timers or sequencers, nice wooden case, and a kick ass modular look.