Sony KP46WT510 picture goes back and fortto horizontal color bars

My five year old Sony projection TV suddenly started going between a good picture and color (R+G+B), thin, varying horizontal bars. Sound is fine. I disconnected the cable box, etc. so that CATV now goes directly to the TV, but no change. Prior to that test I tried a DVD and it worked fine, but the problem returns when back on CATV. Seems to be horrible when cold (~95% of the time), and less when warm (~25%, after 15 minutes or so). Thanks for your help!