820-01841 (2019 15" MBP) - Issue with display switching and going out.

[Thomas]

Hi all,

I have no idea were to start with this MLB. The issue is, the MacBook will boot to OS and show internal display and external only with external monitor connected. Once the external monitor is unplugged the internal LCD goes out. Basically the MacBook can be used normally if an external display is plugged in all the time. I already installed the Logic Board into a known perfect working chassis/lcd assembly and the same issue persists. The Logic Board has an issue and I do not know where to start. I check to see if any components are missing and all is perfect. This Logic Board is in mint condition with no physical damage.

I made a video so ya'll can see the issue.

IMG_9172.MOV

drive.google.com

Any idea's???

 

[2informaticos]

Looks like iGPU problem.
When external monitor is connected, dGPU is forced and it sends video internal and external.

Any history available?
Check if R9850/51 and R9819 switch the voltage accordingly.
May be a problem with U9850 (damaged IG input), or CPU doesn't deliver video to corresponding lines.

 

[Thomas]

This MacBook came from another shop. They said it was showing black screen but when plug in external that the internal video shows. The internal video only shows in OS if you start the machine with the external monitor already plugged in. Once the external is unplugged the internal video goes out, if you try to plug the external back in the video won't switch to either internal or external. The machine needs to start with the external already plugged in to get any video in the OS. If start machine without external the internal video only works in boot menu/ during apple logo then goes out when reaches OS. They tried a good working LCD assembly & same issue. I also confirmed with my own chassis/ LCD assembly and the problem is the same.

R9850/51 = 4.6k
R9819 = 2.2k
U9850 replaced & issues persist, same exact symptom.

At startup/boot menu video shows fine (without external connected)
DP_INT_IG_HPD_R = 3.3v
DP_INT_IG_HPD = 3.3v
DP_INT_EG_HPD_R = 2.9v
DP_INT_EG_HPD = 2.5v

When boot show apple logo on internal then when go into OS internal video goes black (without external connected)
DP_INT_IG_HPD_R = 3.0v
DP_INT_IG_HPD = 2.8v
DP_INT_EG_HPD_R = 0v
DP_INT_EG_HPD = 0v

Maybe issue with U1200? Any other idea's?

 

[2informaticos]

Test starting in safe mode.
Do PRAM and SMC reset, just in case.
You can also save data and try DFU restore.

 

[Thomas]

Prior to asking for help on here, I already DFU restored the machine fully.
I did try PRAM as well.
Issue persists. I know it's a hardware failure somewhere on the Logic Board, but that is all I know.

 

[Thomas]

I tried safe mode and the MacBook boots to OS with internal display.

 

[2informaticos]

Then must be a problem with one graphics driver, which is not loaded into safe mode.
If machine always start correctly with external monitor connected, then I suppose the problem is caused by iGPU driver.

 

[Thomas]

What do you suggest I try next because I already reloaded the OS fresh to make sure not OS software issue.

 

[2informaticos]

iGPU is part of CPU.
Think if is worth to change it...

 

[Thomas]

Ok, I will try U1200 first and then if that fails I will try a CPU after.
It is worth it because MLB is 64GB ram 2TB SSD. When I have an exact CPU available I will try and report back here with the results. For now I set it aside waiting for the perfect donor.

I have only done CPU replacements on T2 machines using exact CPU. I do not know the repercussions of upgrading or downgrading a CPU on a T2 MLB.

Thanks for your help so far.