Help! Bridgeport Interact Series 1 MK 2 with Contraves spindle drive.

I have a Bridgeport series one mark 2 Interact with TNC151 and a Contraves spindle drive. I have no circuit for the contraves bridgeport installation, as my manual only has the KTK drive set up. I did manage to get the service manual PDF for the Contraves off the Contraves website, which includes a full schematic of the CRU and main PCBs, however my BP's Contraves spindle box has an optional card installed labeled "FRU", this is where the S Analogue voltage is delivered. I would like to know what this board does, and how to adjust it. My guess is it does some kind of signal shaping that the TNC151 can't manage?

I have a 4kW RPC, and it is quite okay to run the spindle up to 3750 rpm with this, but you have to set the Analogue Spindle Slope (MP168) to a very low value so the spindle spins up over a couple of seconds, I am fine with this for what I do. The issue I have is that the Contraves card can lock up if I set it's internal slope Lin pot too high and the TNC151 does not know the card has tripped, the asterix keeps flashing. I am convinced there is a wiring problem and this should cause a spindle fault. A second problem is that an M05 command over 1000 rpm appears to slam the spindle brake, sounds like a mallet is hitting the machine. However, the machine does not reset and seems quite happy mechanically.

-Hazel