Just received my Duex5. The power connection on the face and back of the PCB is clearly marked + and -. On the back of the board the + is marked GND and the - is marked VIN? I guess I can verify GND with a meter.
Thanks for spotting this. I just checked my DueX5. The GND and VIN markings on the underside of the board are incorrect and should be swapped over. The + and - markings are correct on both sides of the board. I'll add a note about this to the wiki.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].