THE screen on my Zenith m52w56lcd tv is dim, has

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I have the same exact TV, with the same problem!
I found out that Zenith has a class action litigation open thru July 2010
Your Optic Light Engine is Defective and Zenith has to replace it for free
Or give you a new 50" Plasma or 44" LCD.
Here is the link with all the details ** http://www.zenithservice.com/index_b2c.jsp
Call the service center and let them know what your problem is and that you know
about the litigation. They will have a tech call you and troubleshoot it over the phone.
Then they will order the Light Engine and have a Tech come to your house and
replace it. It will cost you nothing!!!

Your light engine is contaminated with dirt. This is a common problem especially in houses where someone smokes. The light engine will have to be replaced.

Hopefully, you have an extended warranty. if not--figure at LEAST 600 to fix.