The MTI tells me you have the KTK spindle drive. Does the one LED on the MTI card light up? It should, and if it does not you will not have a field voltage at the motor.
The thyristor board also has LEDs on all the gates. The top board can be swung down to view these when (if) the spindle is give a command to rotate.
BTW, there is no parts, no support, and no repair by KTK of this drive. They consider it obsolete. EMI-inc.net has a replacement drive, but it is pricey.
I have a lot of notes on this drive, including a BPT set of notes on repair and the original KTK manual. Just need a email address.