RepRapPro Mendel 3 Tricolour (December of 2015-likely one of the last ones shipped).
Hopefully someone can help me out; I'm stuck.
I have a Duet 0.6 with Duex4 board it was working without fail in tricolour then turned off for several months. Upon restarting the unit and attempting the G32 command the Z axis motors instantly shuddered and acted erratically. After reading through the forums I thought the stepper driver failed, so I bought a new Duet 0.6 board and scaled the machine down to a single nozzle (well disconnected the Duex4). Replaced the firmware to 1.09 (latest), replaced the SD Image back to original, and essentially started over. To my surprise the Z axis shuddered immediately with the new board.
Things I've tried:
Exchanged the Z wires for the X-Y stepper's wires, then the X-Y shuddered.
Plugged the Z motors individually into the Duet; individually they operate correctly.
Pulled the 5V PCB board that places the steppers in series to check their connections (fine)
Used a brand new stepper and replaced each motor one at a time (shudders)
Traced each wire individually from board to stepper (continuity)
Replaced the firmware and SD Image back to original files (shudders)
Board heats up, nozzle heats up, X and Y steppers operate normal
There's 12.15V and 4.94V on the board
The Z axis steppers will seize after any command until the stop command is given then they'll free up.
I'd like to share the solution to the problem. The molex connection between the main "z" connection on the board and the attached board placing the motors in series had a broken female connection inside the molex. Too easy and very frustrating to find!