Emco VMC-100

I was wondering if anyone has experience of setting up a VMC-100. I
bought the machine knowing it had several faults including bad
electronics but I now have all 3 axis moving and the machine is able
to reference. The problem now is that if I try to either start the
spindle or rotate the tool shop the servo drive (aux) psu contactor
drops out and a H15 LED alarm (position overrun) is indicated on the
servo amp control board, once the aux psu drops out then I get a
refence alarm 460 and I'm back to square one. I spoke with a machine
service company and their advice was to reload MSD which I did but
made no difference. Can anyone shed any light as to what could be
causing this?

Thanks,
Paul