820-3662 No Backlight

[appleonarim]

Hello

No liquid damage signs on board but backlight not working.

PPBUS_SW_BKL= 0V
BKLT_EN= 3.3V
PPBUS_SW_LCDBKLT_PWR = 12V
BKLT_EN = 3.3V
LCDBKLT_EN = 12V
PP5V_S0-BKLT_VDDA = 5V
PP5V_S0-BKLT_VDDD = 5V

try to replace u7701 and u7750 also from donor board but nothing changed
what can i check next step?

 

[dukefawks]

Backlight is controlled by the LCD through I2C bus. Try a know good LCD assembly first. Have you checked for an image with a flashlight?

 

[appleonarim]

Yes duke i can see question mark in folder. Tried another LCD assembly nothing changed.

 

[dukefawks]

Was the LCD assembly from a 2014 or newer machine. The older ones are not compatible. Did you check SMC_LID? Also 12V on LCDBKLT_EN, I'm not sure but common sense says it should not be higher than 3V.

 

[appleonarim]

Hi
SMC_LID is 3.3V, if i understand correctly voltage is under 0.5V SMC_LID is enable so LCD backlight ll be close .


What is problem I cant understand U7701,U7750 and q7706 changed from donor board.