If you are using a PMDX-107 with your PMDX-126, then it sounds like you have the signals on the wrong pins.
The PMDX-107 expects the PWM signal on Pin 16 and the Direction signal on Pin 14. Optionally the PMDX-107 can also monitor the Pin 17 "Charge Pump" as a safety measure.
When using the PMDX-107 you do not need a "Motor ON" signal, the PMDX-107 monitors the PWM and turns the motor on when the PWM is pulsing. There is one quirk that can happen. If the S command asks for exactly the maximum for a pulley, Mach3 will generate a solid signal that never pulses if using the parallel port driver. In this case the PMDX-107 does not see any pulses and does not turn on. Not sure is this is also true for a SmoothStepper. Work around for this is to make your max for the pulley be 1 more RPM that the highest S command that you issue, i.e. for a 24000 RPM router spindle set the pulley max range to 24001.
