Sorted, many thanks. Not exactly sure what I did differently this time but I ended up with a different result - PanelDue5i is working!
When I removed the unit I checked the cable and during my belling out a crimp popped out, the connection looked fine but when I tested it it showed open circuit, 50/50 chance for where the bad end was and I lost, it was the end on the motherboard end. Two crimps later and a firmware update and all good.
Tomorrow is calibration of extruders and fun with bed levelling.