Xpro v3 A-axis pot doesn't change current

Hi there, I'd bought xpro v3 controller in January 2018.
Now I come to assemble it and connect to stepper motors.

I found that pot on A axis do nearly nothing.
When it crancked down stepper motor still gets current, when I turn it up completely stepper doesn't get enough current.

I can make y axis run smooth, but when I connect stepper motor to A - I hear and feel chatting and grinding in motor

 

As walk around I connect both Y-axis steppers to Y connector