Top screen gets brighter when console it's completely open

Hello guys, have an old 3ds xl that recently started showing top screen's brightness at maximum while lower screens works perfectly (additionally if I change the brightness in the settings it changes correctly in the two screen when the console isn't completely open, if I open the 3ds screen to the fullest then the top screen's brightness goes up and if I try to change the brightness in that state the console turns off with a popping sound).

So I'd tear down the 3ds and reattached the speaker, camera and upper LCD ribbons but the problem was still there.

Then I will gladly accept any help :)

PD: I actually have the LCD's back side exposed to see the ribbon more carefully.