Dell Latitude 7420 2-in1 display error strange lines

[ongobongo]

Hi guys,
I have another problematic laptop here, a Dell Latitude 7420 2-in-1 with touch display.
Motherboard is Compal LA-K371P Rev.3.0.
The laptop has a strange display problem, see attachment for more details. This problem is not windows related, as soon as you start the display has those lines even in the Bios. If i attach an external monitor, the lines do not appear there.
I was able to get my hands on a second display, but the problem persists, so it seems to be something different.
any ideas?

[Slavol]

Hi, did you manage to solve the problem? I have the same and I don't know where to start diagnostics. Thanks in advance

[ongobongo]

Yes I was able to fix it but it's as simple as it gets, it's the display. The problem will be to get a working replacement. New, if you can get it, it's damn expensive. I bought 3 in total, all used and described as working. Interestingly, 2 of them turned out with the exact same problem. So it is either a standard failure of those panels or something went pretty wrong during shipping. The last one I bought with a photo that showed the display working without lines and it worked in mine.
Good luck with finding a replacement