MOberdick
New member
So I have a 820-3476 board I bought off of eBay with no backlight and its been kinda throwing me for a loop for a little while now. The backlight circuit looks slightly different than previous models with the 1st transistor (at the bottom of the first voltage divider) being integrated with the U7700? At least thats what it looks like... Anyways, the area looked pretty messed up so I went ahead and replaced U7700, both R7731 and R7732 on the feedback trace, and the D7710 diode (all visually looked like crap). Still no backlight. I do have 3.3v on the enable pin of U7700 however Q7700 isn't opening because there is 12.56v on pin 4, and also 12.46v on pin 3 (too much) which is why I'm assuming the backlight isn't kicking on. I've confirmed the resistance on both resistors for the first voltage divider and they're giving proper readings.. what am I overlooking?? I'm leaning towards my doner board had a bad U7700 chip that I grabbed.. Ideas?