I have the same computer and same problem. I have replaced the inverter and the LCD screen. I have reset the p+r+apple+alt. I have adjusted all settings related to the screen. THere is no backlight!! I used a different pc and plugged the new AND old screens into the inverter to test the backlights and both worked. I used a digital multi-meter to record the voltage values for all of the cables connected to the ribbon that goes through the hinge to the inverter. On the board and after passing into the inverter they are all the same, meaning that the cable is performing.

I read the info for the mod link above but it is for an older model of macbook. The A1150 model uses a different color scheme and the voltgage readouts are a bit different.

Understanding that there is a 5v cable on the ribbon I took the closest one I could find, 3.25v and jumped it to either of the two cables that read 0v to see if one represented the dimmer. By sending 3.25v signal through what might have been a dead dimmer signal would have started the backlight. None of my experiments worked. I'm very persistent and don't want to give up on this. If anyone can provide a technical answer or fix I would appreciate it. The computer can still be used as a desktop with an external monitor but that defeats the purpose of an overpriced laptop.