56" Zenith Projection TV....wierd problem

I am encountering a strange problem when viewing my tv.After about an hour of watching,the screen becomes distorted.Screen is 3/4 the size of screen and wavy.I turn my tv off for like a half hour,than back on,and it is fine for another hour,than same thing happens.Also,seems like I'm losing blue color.Anything I can fine tune or does it sound like a board problem?Thanks for any info.

btw...I had a board replaced last year due to loss of blue color.Maybe same problem.