820-4924 - No Backlight

[null]

Clean board and I can see the apple logo, however, no BL.

Already replaced the U7700, but still. I do have the enable, nut 0V on the PPVOUT_S0_LCDBKLT.

W/ the screen Plugged:
U7700:
Pin 5-18 = 5V
PPVOUT_S0_LCDBKLT = 0V / Diode Mode 0.31
PPVOUT_S0_KBDBKLT = 5V
BKLT_EN_R = 3.2V
LCDBKLT_EN_L = 12.38V

Q7700
Pin4 = 12.56V
Pin 1-2-5-6 = 0.34V

Yes, i replaced the Q7700 Just in case, however, still.
The fuse is fine.

 

[2informaticos]

Try another compatible LCD assembly.
Backlight level is adjusted through I2C SCL/SDA lines; between LCD and U7700.
Be sure all R7750-53 are good.

BKLT_SD must be 0V, to control Q7700.

 

[null]

I tried with a different screen, still.
Also the R7750 and 53 Seems fine.

 

[2informaticos]

There are 4 resistors; I wrote R7750-53, not R7750/53...

Post voltage and diode mode on SCL/SDA lines.

 

[null]

R7750 to R7753 all good.
SCL/SDA = 0.555 Diode Mode - 5V

 

[2informaticos]

You didn't clarify BKLT_SD level yet.

Check voltage and diode mode on I2C_TCON_SCL/SDA lines.
Pay atention to R5350/51.

 

[null]

I2C_TCON_SCL/SDA = 0.734 - 3.1V and goes to 0 after a couple seconds.
R5350/51 = 2.0K
BKLT_SD = R7702 Pin2 = 63.4K = 12.41V

 

[2informaticos]

Did you try compatible LCD assembly for sure?
Must be from 2015...

 

[null]

Yes, i did. With 3 Different 2015 LCD Assembly.

 

[2informaticos]

Press backlight keys and check for activity on I2C_TCON and I2C_BKLT buses with o-scope.
Check if at least DC voltage on EDP_BKLT_PWM varies...