Quote Originally Posted by DaveB View Post
Possible problem with X-Axis cable. That's why QiDi ships a spare with the machine. Use of a cable chain can significantly reduce the frequency of a problem with this cable.
Also check that stepper driver modules are securely plugged into motherboard, and that the stepper drive cables are well seated in the motherboard and in the stepper motors.
(Insert sound of hammer striking nail on head.)

'Twas the x-axis cable with an intermittent internal break, and a loose module, and a stepper drive cable probably damaged in the troubleshooting of the others. Thanks for the pro-tips!