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

KC Micro Tronix

KC Micro Tronix

Member
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?
 
KC Micro Tronix

KC Micro Tronix

Member
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.
 
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