820-02016 Air M1 (no image, then after some repair No backlight)

[KC Micro Tronix]

Was given to me as "no image"
LP679 melt down and UP700 smoked!
After the repair I got image but no back light.

Trouble shooting no back light.
UP800 / swapped
BKLT_EN_R 1.8v
BKLT_SD 12V "not pulling down" Resistors checked.
QP800 tested / swapped.
power rails present.

I have Isolated BKLT_SD from
QP800. voltage floats to 4v on BKLT_SD and 10v shows up on the buck converter so QP800 turned on.

UP800 even when replaced and getting a enable signal from the PMIC UP800 refuses to pull down BKLT_SD and turn on QP800 and pulse QP801. What am I missing here?

 

[2informaticos]

Apart of enable signal, UP800 requires correct I2C_BKLT_SCL/SDA communication with LCD assembly.

 

[KC Micro Tronix]

I ohm checked the two SDA lines to JP600
I2C_DISP_BKLT_SCL
I2C_DISP_BKLT_SDA
(good)
.
the SDA lines make good contact with JP600 The resistors on those lines. RP850-RP853 are all good. Not sure what else I can check here.
I will get out the scope.

 

[KC Micro Tronix]

I am just going to trash this machine and move in

 

[2informaticos]

Did you try known good LCD assembly?