Tweakie.
Before reading your latest mail I found a record of how I had set up mach3 originally in 2007 and noted some differences from my current settings.
I put in the 2007 settings and everything worked!.
The main difference was that the motor output step and direction pins were in the wrong columns ( if I make myself clear).
spindle was selected - step pin = 1, dir. = 17, tick, tick 1,1
input signal used was - timing enabled - port 1, pin 15, tick, X, 0
output signals used - enable#1 - tick, 1, 14, tick
output#1 - tick, 1, 16, tick
Testing the system the spindle reacted to M3,M4,M5 as it should but the spindle started to turn only when a speed of 3600 or higher was requested.
So I messed about and succeeded in stopping the spindle rotating with M3!!!, still OK with M4. Do not know what I altered but the red LED on spindle electronics permanently ON.
With M4 the red LED flashes in tune with speed of rotation.
Further work required to solve this one. NOTE record all changes made in future.
At least it is not a faulty computer, just an embarrassed operator.
Malcolm