A1989 (820-00850-A) - No Image/No Backlight

[HeyWatchOutDude]

Hi,

I have here an A1989 with no image/no backlight.

Water damage:
-> water_damage.png

Note:
- External display shows image - so the internal GPU is working fine.
- " EDP_INT_AUX_N " = 0.007 (diode mode) / 3.4ohms to ground - Is the CPU bad?
- Heat shield on LCD getting warm (IMG_0615.jpg)
- I have tested several screens - no image/no backlight on all of them
- Logicboard is booting fine / trackpad clicking / touchbar is working / caps lock - green light

Additional issue:
- High fan spin on the left side (all sensors are present)

 

[2informaticos]

"External display shows image - so the internal GPU is working fine."
Not really true; tis board doesn't have dedicated GPU.

iGPU core and external video output work, but internal eDP output is damaged; auxiliary channel shorted to ground.
This is the result of direct connection between J8500 and CPU; no series caps present.
There is no way to solve this issue; apart of changing CPU...

 

[HeyWatchOutDude]

Ok, thanks for your help!

 

[HeyWatchOutDude]

I removed a CPU from a donor board …. Sadly I lost one cap/resistor on the back of the CPU. Any idea what’s the value of it?

 

[2informaticos]

Check boardview/schematic...

 

[HeyWatchOutDude]

it’s the underside of the CPU, where should I get the schematics/boardview?

 

[2informaticos]

820-00850.rar

drive.google.com