Samsung PN42B450 horizontal lines on black screen

[YamahaFreak]

Update: I replaced the power supply board with a known good one, and that did NOT fix the problem. No change. For good measure, I also checked and re-seated all panel ribbons between the panel and the buffer, as well as the connectors between the buffer and Y-Main. No change at all.

Now, the only things I haven't swapped are the mainboard and the buffer board...other than the cables and interconnects! Oh, and the X-main and related, since I wouldn't suspect those with a horizontal lines issue. Mainboard costs twice as much as the power supply...I might have to put this TV on the back burner until I can afford $100 for a mainboard. Should I try swapping the buffer out?

EDIT: Made some YouTube videos that show the problem in a bit more detail than a single still picture can.

https://youtu.be/PvZJqG2dAMw?si=7vky_3871suGganF

https://youtu.be/tKXAIKemB8w?si=14tYpfIuKPMDURjv