I had the spindle running on an old parallel port system instead of the 4th axis(A).  The spindle drive is the DMM DYN4 drive. The computer crashed so I bought a smooth stepper board from CNC4pc.  I am using Mach3 the USB smooth stepper board and the DYN4 Servo board with a 86H-DHt-A6MK1 1KW AC servo motor.  I have been trying to set it up with the smooth stepper but not having any luck.  I purchased the C6 Variable seed control board, no luck.  I have the X, Y, Z and A axis working fine.  Just cant get my head around setting up the spindle.  The DYN4 can use step and direction or PWM.  Either is fine for me, just want to get back to making parts.  Any help appreciated. 

If using a servo on the spindle that takes step and direction signals; you should just control it using step and direction, not PWM.  Check this setup:
https://www.cnc4pc.com/blog/post/configure-an-step-and-direction-servo-as-spindle-on-mach4-using-the-ethernet-smooth-stepper-and-c82

Arturo Duncan
https://cnc4pc.com