Hi Jeff,
Thanks for your input.
I actually ended up a shorter route (pun). I was in the shed without shoes (yes I know). Anyway, I touched the rails and got a buzz. Touched the control box and got a buzz, and touched the computer box and got a buzz. I fixed the earth in the control box that had broken loose in the recent move and fixed that problem.
Still had crashes, though, must to my annoyance.
My wife comes in and says,"Why don't you try plugging the power board into a separate socket from the computer?"
Humph, what does she know!
Well the crashes have stopped. Pulling 4-9 amps off a 10 amp domestic circuit must have been enough to upset the computer.
Anyway, Mach 3 was never to blame, nor was the link to Cut 3D. I got to this conclusion early in the piece by testing simulated runs with and without Cut 3D, and with and without the power board on.
Many thanks for your interest and support.
Regards
Red