Xerox 820-II troubleshooting - need advice

[Tony Duell]

> To see if your 820 mainboard is at fault, try driving the keyboard 
> lines with the output of a PC's parallel port (not possible with a 
> "real" computer like a Mac).

But certainly possible with real computers like PDP8s, PDP11s, PERQs, 
HP9000/200s, machines with HPIB or HPIL ports (+ the right interface 
converter), Commodores (most had user ports IIRC), BBC micros, etc, etc, etc

Alternatively, can't you see if the existing keyboard is sending anything 
using a logic probe?

-tony