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I have a 51" Samsung D7000 plasma that was manufactured in October 2011 and purchased in December 2011. I've had no issues with it until September 2015 when it made a loud "pop" and the screen would no longer power on. I installed (supposedly) new Y-sustain and Y-buffer boards and the TV has been running fine since then.

Shortly after this repair, however, I began to notice that when watching very dark content there is a horizontal line visible halfway down the screen. This is also evident, to a lesser extent, when watching very bright content. The line is not any particular color, but really just the edge between the top half and the bottom half of the screen, which are now two different brightnesses. As you can see from the attached photo (which looks a lot worse than what I'd actually see, but gives a good sense of the variations in brightness) the top half is brighter but not in its entirety. It's only from looking at this that I also realize that the two halves seem to be mirrored inverses of each other.

I have the TV opened up to correct the red banding problem when viewing white/bright content, which is a problem I remember seeing every now and then before replacing the two boards, but seemed to become much more intense after the repair. Increasing Vs from 207 to 212.5 VDC has eliminated the redness problem, and I'm hoping I can fix this brightness issue now, too. I have confirmed that Va, Vsc, and Ve all match the sticker on the chassis. I have disconnected and reconnected the Y-buffer to the panel, making sure all six connectors were snug and it made no difference.

In all my Googling I've only come across two people on one post with what sounded like this same problem, but no culprit or solution was identified. I'm wondering if this is possibly the result of burn-in, but the only thing I can think of that could cause that perfect line is maybe a bit too much 2-player Mario Kart a few years ago, but I'm sure I would have noticed that before the board replacement because it's about all I see since then. I've tried the scrolling pattern every now and then and it doesn't seem to do anything, but I think the auto power off was interfering so I've got that disabled and will run the pattern overnight. Is there anything else I can try or check? Could something be wrong with the Y-buffer that's causing this? Thanks for any insights.
 

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