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Looks like the flex cable contact is bad, I have tried to fix it and inserted again. Now I don't see the backlight anymore, Basically, EDP_BKLT_EN is missing. But still, there is a chime sound. When I bypassed Q7707 the entire screen is white.
smc_lid - I have disconnected the flex cable --- > Voltage is 3.4V when the display LID is open. Voltage is 0 when the LID is closed. Still, I don't see a backlight. I am testing without flex able. And I have ordered a new cable. Does this cable and backlight are related ???
I don't think there is any image on the screen. At least I can't see anything on the screen. But there is 24.7V on PPHV_S0SW_LCDBKLT. Apple logo light at the backside of the lid is glowing now. DP_INT_HPD is continuously varying between 2.45V to 2.55V.
So the backlight circuit works; 25V is correct output.
Try known good working LCD assembly.
If still no image, check diode mode to ground on all data video lines.
Also be sure all the caps are in place and have good traces.
I have removed and connected the board , hdd and all the connections. Now good news is image and backlight is there. I suspect something were wrong with smc/Pram memory. The touchpad flex cable might had a short internally. I don’t want to try this broken cable anymore. Ordered new one. Waiting for it.