Hi Bernard, Ok well, to be honest, and as expected, I've got a feeling this controller can not control the spindle speed from mach3. For Mach3 to control the spindle speed then it must have a spindle card installed or the breakout board which can provide a speed reference voltage. However to be sure we will need to look inside the controller at the boards to see what you have. So if you can take the lid off and get some good pics it will help.

However, even if it doesn't have speed reference voltage it's still possible to control the ON/OFF from Mach3 which is still very handy.