820-1987 Image no Backlight.

[grmacs]

Liquid damage to backlight area on board. replaced shorted cap C8462 and F8400.

LCDBKLT_EN_L: =12.6V
BKLT SCL/SDA= 5.1V
BKLT EN R =3.3V
PP5V_S0_BKLT_D/A= 5V
DP_INT_HPD= goes to 3.3V
R8450/1/2/3 all good resistance and diode values check out
PPVOUT_S0_LCDBKLT_F = diode value is low at .12 - would that have any affect? I'm guessing there's another weak cap but figured I need to resolve LCDBKLT_EN_L being high first

I tried a different working display also.

 

[2informaticos]

0.12 is too low; something else affected by liquid spill.

 

[grmacs]

I'm guessing another bad cap. would that be related or potential cause of LCDBKLT_EN_L: =12.6V?

 

[2informaticos]

If U8400 detects output leakage, will block Q8400.

 

[grmacs]

Excellent info. Thank you! I'll fix that and see what happens!

 

[grmacs]

Replaced a few more caps on PPVOUT_S0_LCDBKLT_F after burnig up some more caps. DIode mode there is consistently 1.12 there. Now I'm getting backlight briefly on initial power up and voltage will remain at 54V then drops to 12V and then down to basically zero. KBD backlight voltages seem to stay steady at 5V.

 

[grmacs]

Have you seen or heard of temporary backlight at initial power up?

 

[2informaticos]

There must be something more affected by corrosion.