I know nothing about these machine so can't be much help. Does the keyboard work in a similar way to a BBC? Documents for the latter might be easier to find on the web.
That is unusual though. In most machines the only symptom of a faulty keyboard is that keys don't work.
"donor electron". I'm not sure if that was a deliberate pun or not but I like it.
I've just had an exciting time (-NOT) regarding a keyboard and one of my Colour Genies. But that's another story...