before you do that, swap the step and dir leads from your x axis driver to your z axis driver. Does the fault move as well, or does it stay with the Z axis. Then jog the Z axis, using the X axis jogger and vica versa
If the fault moves, the fault is with your Z driver card not seeing the dir signal. If the fault does not move then the fault lies between your computer (which you say you have checked) and the breakout board.