Flickering TV, lines on the bottom

Hey,

My TV shows a flickering screen with multiple lines. At first some minor flickering occurred and from use to use it worsened. At current state no usable image is recognizable. I opened it up and checked all Connections and also tested, if the backlight was the issue. Non of that fixed my problem. I ordered a replacement PSU board und the TV seemed to work fine again. After about 30min of use the original problem occurred again. I also tried a new mainboard afterwards and nothing seems to fix my issue.