I serviced dead backlight issue last week, more on that here: http://forums.macrumors.com/showthread.php?p=16361152#post16361152
there are three types of voltages going in the inverter- 24V DC main voltage, backlight ON/OFF signal (I refer that as backlight-enable in the post on macrumors forum) that should be 2-5.5V DC to get the backlight, and Backglight-intensity voltage (on the inverter pcb marked as VBR) that should be between 0-3.3V DC. check these and tell us your measurements to trace down the problem.