820-01987 No backlight / Has image

[bls951]

I have an 820-01987 with no backlight. It had some liquid damage in the backlight circuit around L8420.That was cleaned up and traces are good now.
There wasn't any liquid damage around u8400.

PPVOUT_S0_LCDBKLT - 0V with no short.
BKLT_SDA - 5v
BKLT_SCL - 5v
PP5V_S0_BKLT_A - 5v
PP5V_S0_BKLT_D - 5v
LCDBKLT_SW - 0v
LCDBKLT_FB - 0V
PPVIN_S0SW_LCDBKLT_R - 12.6v
LCDBKLT_EN-L - 12.5v
BKLT_SD - 12.4v
EDP_BKLT_EN - 3v before dropping to 0v once an image appears on the screen


I am using known good LCD + LCD cable to check the board.

Any help would be appreciated. Thanks

 

[2informaticos]

Check R8431/32 and their traces.
Also check Q8401 and R8433.

BKLT_EN_R has 3V too?
Change U8400, just in case.

 

[bls951]

R8431/32 are good and so are it's traces.
R8433 is good and so are their traces. Q8401 seemed good as well, swapped anyways. Traces for it are good too.

BKLT_EN_R - Has 3V for initially before going to 0v
Changed U8400 a couple times as well with no change.

 

[2informaticos]

BKLT_EN must remain high (3V).

Check traces and continuity fro all components in the corroded area.
Just in case, change both L/D8410.

Be sure all resistors in backlight area have correct values.