So, i did the same on other laptop. Laptop still doesn't see the Navi board. Two ways - corrupted flash or electronic problem on board. Unfortunately i can't find circuit scheme the navi board in the net. Maybe someone have similar?

In the meantime i start compare circuit diagrams other units with my. For this moment i see the navi board from 7220 doesn't fit to 7240. Different connectors to main unit board.
I'll go to tamper;-)