820-00426 no backlight

[ytesfay80]

I have this machine that had liquid damage in the area of the lcd connector and thunderbolt ports. The connector looks fine and I have ultrasonic'd the board already. The machine turns on and chimes but I get no backlight. When I shine a flashlight I can see an image on the screen. I have tried a PRAM reset but that did not work. I thought the LCD cable might have been the issue so I tried with another cable plugged in but still no backlight.

On backlight output at the LCD connector I get 0v. On pins 3/4 of Q7706 I get 12.56v and 12.44v but 0v on the output pins 1/2/5/6. R7701/2 measure proper resistance. SMC_LID is 3.4v
I replaced U7701 but that still did not solve the issue.

I don't have another display assembly that I can test this with so is there anything I can check for to figure out why there is no backlight?

 

[dukefawks]

Diode mode on LCD connector?

 

[ytesfay80]

In diode mode with red probe on ground and black on Pin 1 of the LCD connector I got 1.20v. Not sure why the number is so high but that is without the charger plugged in and I got that value with and without the LCD plugged in.

 

[dukefawks]

I need pins 1-10 in diode mode.

 

[ytesfay80]

With LCD connected. Diode Mode

Pin 1 -1.21v
Pin 2 - Unconnected
Pin 3 - 0.493v
Pin 4 - 0.115v
Pin 5 - 0.448v
Pin 6 - 0.50v
Pin 7 - 0.495v
Pin 8 - 0.503v
Pin 9 - 0.492v
Pin 10 - 0.613v

 

[dukefawks]

I need it without LCD connected.

 

[ytesfay80]

Okay diode mode measurements without lcd connected.

Pin 1 -1.22v
Pin 2 - Unconnected
Pin 3 - 0.53v
Pin 4 - 0.529v
Pin 5 - 0.636v
Pin 6 - 1.361v
Pin 7 - 1.365v
Pin 8 - 0.614v
Pin 9 - 0.597v
Pin 10 - 0.62v

 

[ytesfay80]

dukefawks were these diode mode readings able to help diagnose this?

 

[ytesfay80]

I just replaced Q7706 but still I get no backlight. I'm not sure what else to do.

 

[ytesfay80]

Does anyone have an idea on what the issue could be with this based on the readings? I'm hoping the display assembly is not the issue here.
larossmann aprendiz