Hi all

Issue:
Long standing mill x/y/z, now adding a 4th axis.
When I power up the BOB all is good, stepper motors startup and control the axis as expected including A-axis
I can home the machine and motors behave except no "homing" from A-axis
Jogging all fine on x/y/z but as soon as I jog A-axis the motor goes slack and I can freely turn it by hand. Small vibrations felt on the motor but no apparent movement.

Config:
Mach3 3.043.066 on Windows 7 32 bit
Smoothstepper USB driving KTA-205 4 axis BOB, same physical kit for years
3:1 belt drive reduction on a 200 step motor, 1/2 step microstepping on a M542H Chinese knockoff driver
A-axis tuning set to 3.333 steps per based on 200 steps x 2 for the microstep x 3 for the driver reduction = 1200 / 360 degrees = 3.333
A-axis angular ON
360 rotation ON
Rotational soft limits ON
Softlimit Amax = 360, Amin = -360
Toolpath axis of rotation = X
Axis rotations ON

Been driving me nuts for a week now, any thoughts ?

Thanks

David