Sounds like you either have a bad LED driver or the fuse links are blown on the logic board.
Do you have an DVM to test the fuses? The fuses are similar to the resistors they will have a dot or an O marking and they should be near the LVDS connector.
Update
U9701 is the LED driver. On this board I believe it is a custom Apple driver codenamed GOSHAWK. F9800 is the fuse.