Black screen even after some fixing.

Hello,

I got an S4 mini smartphone from a friend with shattered screen. The phone worked OK, I was able to receive calls, but the screen was all black.

So I changed the LCD+glass for a new one, but it was still the same.

Then I changed the whole motherboard and "power board" with USB connector thinking it could be a SW problem, but the problem is still exactly the same - phone works, but screen is black.

At this point the only parts from original phone are:

battery, proximity/light sesor, SIM/SD slot, mic, speaker, 3.5 jack, cameras

Do you think some of those parts can cause the screen to be black? I tried every common way to fix it like hold power button 1 minute, etc. but nothing works. I also measured the battery and it looks fine.

Thank you for any ideas. At this point I believe the phone might be cursed :D