Referring IC-746 model backlight problem i meet same think newer model. I think that this problem occur Europe model IC-7400 too.
First i change backlight cold cathode lamp but no help. Second i read carefully what it made for IC-746 repairing.
In the metal box has few component witch make cold cathode lamp requiring voltage. There is one bigger transistor what is Q302 2SB1201 PNP transistor. Because there is no enough cooling area in printed circuit board, this transistor go faulty.
I remove it using normal 50W Weller solderstation and desolderbaraid. Next i drill to the metal shield one side (most of all emptiest room) and replace original 2SB1201 to BD650.
Other type is ok if you check 2SB1201 current and voltage values.
It is very important insulate this transistor from metal shield (it is grounded) because all transistor legs have no ground contact !
Then shorten new tr. legs and solder short pieces of wire tr. legs and place where original tr. was.
Put all boards back and front panel to the main body. If all ok there is backlight on radio.
I no take any liability for this repair instruction. You make all you own risk.