A while back, I was suffering from faint purple lines on my plasma display, and the were especially noticeable during dark scenes or transitions.
I consulted this forum, and Mtrycrafts had the following advice:
Try this experiment:
Totally unplug the cable TV/Sat TV from the setup, including the TV. Then send video to the TV and see if those lines are there. I am betting when you unplug the TV the lines will be history. If so, plug the cable TV back and look for the tell tale signs. Then buy this:
http://www.cencom94.com/gpage.html8.html
for all your incoming TV lines. Give us feedback, please.
Here's my feedback -- this little sucker WORKS! The lines are gone. All for about 12 bucks!
Thanks, Mtrycrafts, for that pointer!