Phase 1

Started with getting the datasheet for the microcontroller (TSC87C51). Identifying the power pins and working back to the main header on the PCB. Once those pins had been identified I powered the keyboard with 5VDC checked for excessive current draw and then started probing the rest of the header pins with an oscilloscope looking for activity while pressing a key repeatably.

Couldn't get anything on any of the pins but while I was at it I made sure the oscillator was working - it was so there was nothing left to do but desolder the microcontroller and put it in a EPROM programmer. To my surprise the chip was blank or had its security bit set.

Either way this was a dead end so onto Phase 2.