Hurco BMC25 Spindle Drive Problems

Hello,
I have a Hurco BMC25 1990 VMC. I bought it second hand 18 months ago and have had all sorts of issues with it. Anyway, slowly working through them but the latest is this: I have spindle control issues. I cannot start the spindle manually, you can run the machine in a warm up cycle, but either spindle does not run at all, or spindle runs straight in and constantly at maximum RPM and does not stop. The Ultimax control screen only ever reads ****** in the RPM readout, and altering the manual speed on the controller seems to have no effect. The machine has a yaskawa spindle inverter drive which I have had rebuilt professionally. The RPM is displayed on the LCD of the drive. The spindle Orient for tool change seems to work fine.

Anybody shed any light?

Many thanks in Advance!