00281 - No Backlight, no image, no hints

[down1nit]

Not entirely sure of history, no water damage visible anywhere. Tried the usual SMC/PRAM reset. Bare board boots ok to OS on external.

Screen seems detected, EDP_PANEL_PWR_EN is high as is DP_INT_HPD and SMC_LID. I can't make out an image but I seldom can with these. I looked under the scope for moving LCD pixels etc... Different screen same story (genuine 2017 screen)

I'm not too sure what to check next, backlight is not being enabled, but i've already checked the fuse (fine, 12.56v both sides) and BKLT_EN (missing). No short on PPVOUT Backlight

 

[2informaticos]

Image should come before backlight.
Use powerful flashlight to check for image.

Check diode mode to ground on EDP_AUXCH/INT lines of J8500.
May have a problem with AMUX U9850.

 

[down1nit]

DIode Mode, red on ground:

EDP_AUX both @ .398
EDP_INT_ML_N<0-3> @ .342
every other pin seems ok too

SMC Pullups fine (r5351/r5350)

I have many spare mux chips of course. U gotta keep these in stock lol.

Will report back!

 

[down1nit]

Replaced U9850, same behavior.

 

[2informaticos]

Shouldn't be U9850 issue, with posted readings.

Still can't confirm internal image?
It must appear before backlight comes on.
Keep in mind, to avoid video artefacts, backlight is last enabled when machine turns on; and first disabled, when it turns off.

Change the small video cable.
Also inspect J8500 connections.