Unfortunately it's not the cable. I just managed to fit the ribbon on the control board straight into the back of the parallel port and it's still doing the same.

Is there anybody in the UK who takes this kind of repair job on or is it better to ditch it and build a new controller with bits from Zapp? I was just very happy with how stable the system was. I could throw half a million lines of code at it and it would take it in it's stride.