LCD not lighting up after repair

I have a first Gen iPad 3G 64GB that was water damaged. I had bought it in this condition and decided to attempt to fix it. When I bought it , it was stone dead.

I replaced the battery and digitizer (the previous owner had broken the digitizer cable in attempt to fix it himself).

The good news is that it is now working (ie Itunes can see it, and it makes sound, digitizer works) but the LCD has no backlight. I can make out a faint image on the screen but after a hard reset and an itunes reset there has been no change.

My question is, could it be the LCD cable, the LCD itself or is the logic board damaged or any of the above?

Any advice is appreciated.