Y Axis Drive Intermittent failure


New Farmbot User with a Genesis v1.2

Having some problems with the Y-Axis Drive. It is intermittent. Sometimes the motor has no power. Sometimes it is powered an won’t run. Sometimes (about 1/2 the time) it works fine. There is no event that I can figure out that causes it.

Let’s say the Y axis stops working. If I swap the Y Motor Drive cable to the Z-axis. The motor works fine. (And the Z motor works fine plugged into Y driver). So the motor is working well and there is no binding in the Y gantry track and the belt is tight. Then if I switch the wiring back to the design configuration, it works fine.

Any ideas? Is the stepper driver OK? Does it need adjustment or replacing? Bad cable? Bad connector?