My Samsung PN50B650 plasma tv after 30min-hour turns darker or dims.Picture still looks good but darker.I replaced logic board and power supply board.Also have faint red and green band or vertical bars across the screen.What do I need to fix this.

SOURCE: Black Vertical Lines in screen

All I can tell you is that you maybe have left your T.V. on a channel that didn't move for so long, or maybe someone else did and it burnt the screen. Plasma's run off of plasma gas to create the great picture and they collect on the screen and stick. What you need to do is go to your menu and look for "screen burn protection" and put it on white and let it sit for 20 minutes. All of one color such as white doesn't harm your T.V. The only way anything burns is like a bright white line in front of a black background.

SOURCE: nec plasma tv 42MP4

these plasma vertical black lines are notorious. there's a video of a fix on this plasma tv repair site. good luck!

SOURCE: Red Dots on My Plasma.

Did you get this problem resoslved? I had the same issue a few months ago. I tech came by and took my TV to the shop, a few days later he said it was fixed as they needed to make some adjustments.....The TV has been fine up until a week or so ago and now the red dots have appeared again. Was wondering what happened to yours.

SOURCE: Samsung TV Power Supply Board

I doubt that moisture damaged the SMPS bd.
There are many circuit boards in your set and it will take a trained samsung tech to find the problem.

SOURCE: samsung plasma HPR4272 that had a 4" black vertical line on

There are at least two issues here. First you have bad buffer boards. Second Very possibly a bad X-Main bd and P-Logic bds. Have a trained Samsung tech troubleshoot the set.