Have found that the issue I was having is that the stepper motor does not move properly at all.
I have got the Mini rambo board running on 12v, am using 40nm Nema17 motors. If I take one of the nema motors from the X or Y and plug it into the port of Z, then it does not turn the motor much at all. Rather a bit of a funny grinding noise.
All other ports on the Mini Rambo work as expected, and run very smoothly. Am at the point to start trying to use the machine now to cut some thin MDF and polycarbonate.
Any hints as to what I can try?