I didn't recognise that part number (the randtronics boards in my hurco MD3 are numbered 800D05...), but if it is the randtronics drive then it's almost certain that it's one of the power transistors on that board shorted out (one of the four that are mounted on the heatsink) putting full power the servo in one direction.
Replace
all four of them with Motorola/ON Semi MJ10021 and all will be well. While you're at it replace the electrolytic capacitor next to the rectifier, and make sure that there are no burnt resistors in the power section. When you replace the transistors make sure and put the insulating pads back in (clean them thoroughly or replace them) and check with your meter that there is no continuity between the heatsink and the case of the transistors or you will get a ground fault when you power it up.
One word of advice though, buy the transistors from a reputable component supplier, not from ebay and absolutely not from anywhere in china!
You will most likely need to tune the drive after you've done this, I have the hurco process sheet for this if you need it.
Hope this helps.