Ok. I changed it to USB mode by pressing the mode button (red light). So connecting usb cable (power still provided to FW from camera 4 pin cable)
and adding QHYCFW3 to profile it seems to work. Not really what I want as I already have ZWO EFW which works with this camera but is not
a very neat solution.
Bottom line FW does work but not in 4pin mode.
Any ideas to debug what's gone wrong with 4pin mode appreciated.