Morning,
Firstly can you check what your LIGHT parameter is set to (see page 45 of the Ego9 manual)? If it is too low (1 second or under), then it would permit the backlight to come on when you push a button and then go off after the time that you have specified. To rectify this raise the time to a more appropriate level like 6 seconds.
If that is not the case, then unfortunately everything points to a bad connection somewhere on your board. The only solution to this scenario would be to replace the circuit board in its entirety.
As always, please contact us on:
customerservice@planeteclipse.com or (0161) 8725572 if you require any further assistance.
Kindest regards,
Nicky T
Planet Eclipse