Finally updated the firmware on all machines, looking a tiny bit more powerful than before.

The unit which wouldn't power is now fine.

The unit with the LIBUSB error is still the same after firmware upgrade so looks like that machine isnt going to play ball at all.

I took the lid off and see that the board revision is 1.0 where as the other machine is 1.2.

I've no idea what to unplug / leave plugged to test each board individually.