MacBook 2015: Trackpad, Keyboard AND Display not working

Hello,

I´ve got to repair a friend´s MacBook late 2015 Retina 13”.

Apple Store said the display is broken, but that definitely isn’t the case. I opened it and checked the cables for water damage (there is a minor water damage, keys are a bit sticky.

However…

The keyboard, trackpad and display doesn’t work. It won’t turn on without cheating it by removing the battery connector and plug the power supply in - then the power button works, sometimes. SMC reset is also possible. When it starts up, the display shows the Apple logo for a short time when booting up, then it stays dark, also trackpad and keyboard don’t work. I can observe it booted when I lit through the Apple Logo from behind.

It works normally with external keyboard, mouse and HDMI display. I reinstalled the OS, it seems not to be a software issue.

My suggestions are the Macbook thinks it is closed, or some power issue.

I cannot explain, why Display and Keyboard/Trackpad are faulty simultaneously, these are different cables?

Thanks for your interest. I´m hoping this is kind of a common problem.