… But before, checking if the 24 volt supply to the inverter is present is the first step…
That is maybe a problem. Because the Mk6 has no CCFL but LEDs there is no inverter but a driver board. And I think when one or more LEDs are not working, the whole panel gets no power (24V) for safety reasons. I am not sure about that but I am quite sure.
As I wrote above: PCB03 P005 Pin2 should be 5V but is only 3V!
Regards Michael