Hi luca, in my case, I don't see any black lines (horizontal or vertical) at all. The screen simply jitters/vibrates and sometimes it simply scrolls down about 1/3 and then bounces back to the top. The interesting thing is that the problem is gone as long as I have a keyboard opens, or have the apps (not all) run in full screen mode (any kind of background color). I've installed xkbd which can be minimized to simply two little boxes on the bottom right corner. It works (even when minimized). I'll live with it and hope that it won't get worse. I bought the unit overseas (much cheaper) and got problem getting it serviced under warrantly