Problem with the X axis

I need some help, tonight I was cut a sign out and things were going as they should
I started to get a bit cold turn my back on the machine to light the patio heater, when I looked
back at the router I noticed the gantry was not square to the table, so I hit the Big Red Button.
I thought I had broken a flex coupler or lead screw as that has happened before. Everything checked
out OK so I squared the gantry back up and run it up and down the table a couple of times, no problems.
I'm running two stepper motors on the X axis that are slaved together, after a while I noticed every thing was
OK heading to home/"0"/X- but heading away from home X+ the gantry would twist.
I worked out the the "A" axis motor was turning anti-clock wise, didn't matter what way I jogged. The "X"
motor turned both directions.
I'm using a Gecko G540 stepper drive, so I swapped the "X" and "A" axis lead around and now the "X" axis
will run anti-clock wise.
To me this indicates a problem with the G540, is there anything else that would cause a stepper motor
to only run in one direction when X+ or X- is pushed?
Is the G540 serviceable or is better to get a new one?

Regards,
Ken