Why is the left quarter of my screen black?

I replaced the complete Screen assembly, after the tablet landed uncomfortable on the floor.

Before i replaced it, it was working fine, only the screen glass was cracked.

Now the left quarter or 1/6 or whatever stays black, the backlight is working. Is the graphic card inside the lcd assembly, or is it possible that this was damaged during the repair? I worked very slowly and careful and i am 99%sure i didn't damaged anything, it's wasn't my first repair, i did many phones and notebooks already, but my first tablet.

I checked every cable connection several times and even cleaned everything with 99,9% Isopropanol.

I made a system reset, to assure its a hardware problem.

Now i hope you have an idea how to fix it.

Otherwise i have to send the Display back to China, where they actually have holidays and which takes weeks, even without holidays...

If anyone has an idea where the problem lies, this could help me too maybe, please help me and thanks for your time.

I invested now 200$ and its worse than before. :(