Why is the backlight out?

I have a Macbook Unibody A1342 and the back light to the LCD display is not working. I originally bought this to repair it and was aware of the problem because the previous owner mentioned them. I looked up all the guides and came to the conclusion that it was the fuses that were out because I could hold a light to the back of the laptop where the logo was and see the home screen and wallpaper. Also when I looked at the logic board I saw "gunk" around the fuses. I proceeded to replace the logic board but that did not fix the issue. I then replaced the LCD display and that did not fix the problem. I finally replaced the LCD lvds cable and Im still not getting a light in the back of the laptop. Does anyone out there know what could be the problem here? Again, I've replace the logic board, LCD display, and LCD lvds cable.