A1398 2015 820-00426 No image and display backlight before log in on macOS

[prw07]

Image and display backlight are present while macOS is load but the display turns off before log in. The laptop is working (hear sounds), but without image and backlight. Internal LCD normal is worked in safe mode also when connect external LCD.

I think the problem is with the integrated graphics iGPU.

Is it possible to disable iGPU ?

[mon2]

Force the use of the dGPU.

https://support.apple.com/en-us/1022...ing%20checkbox.

[mon2]

See if this helps - not sure if your logic board has the same fault but worth a viewing:

Macbook Pro A1398 2012 Retina GPU Vcore Failure Repair on board 820-3332 (youtube.com)

[prw07]

See if this helps - not sure if your logic board has the same fault but worth a viewing:

Macbook Pro A1398 2012 Retina GPU Vcore Failure Repair on board 820-3332 (youtube.com)

there is a problem with GPU(external graphics - Nvidia).

in my case, the problem is with iGPU (internal graphics - Intel CPU)

[reformatt]

My understanding is that MAC OS switches to the discrete GPU when it loads. At least, that is what the earlier models did. It's using the internal graphics when in recovery or booting, and only switches to the discrete when the kext's are loaded in MAC OS.

From what I see in the schematic, HDMI and DP (via Thunderbolt) are fed from the discrete GPU. Check if you have output on these and maybe swap out the RIO board too to eliminate it as a cause, as these are often liquid damaged.

[prw07]

My understanding is that MAC OS switches to the discrete GPU when it loads.

No. macOS using the discrete graphics when booting and after switches to the integrated GPU.

[mon2]

Force the use of the dGPU.

https://support.apple.com/en-us/1022...ing%20checkbox.

[prw07]

Force the use of the dGPU.

Thank you. It's worked!!!