Chosen Solution
I have multiple problems on my MacBook Pro 15" A1226. First, the display backlight does not work, however, an external monitor does work. I tried replacing the LED Driver board (bought from iFixit), but the display backlight still does not work. I have not tried replacing the inverter cable since that is unavailable from iFixit (any suggestions for other reputable places to get said cable ?) Not sure what else to try for this display backlight problem. Second, the startup chime is buzzy. Interestingly, when I open the System Preferences: Sound panel, there is NO input or output sound devices listed. I’m open to any suggestions for restoring the sound devices.
Turns out the left I/O board was bad, replacing that cured the no display backlight problem, no sound devices detected, and an unresponsive left-side USB port. Power connector still worked with the bad board which led me to believe that the board was not the problem.
