Need a bit of help.

[cropwell]

It doesn't have to be the DIR line that breaks. On my machine I have had the same problem with the Z axis and on the 3D printer the Y axis has failed twice causing distorted prints. The Y axis is the only one with a rapidly moving cable. The problem in both cases was a motor wire fatiguing at a connector. In both cases I have clamped the wires to remove movement at the connector (after replacing the cables).

I don't know why, but a faulty connection to a motor winding can make the stepper go in one direction intermittently.

Cheers,

Rob