Devices: All projection TV's (HD or analog), especially Samsung
If its a Samsung HCN653W (or similar model), the first thing to try is the menu option named "Magic Focus", which tunes the set's focus.
Otherwise, it sounds like a job for
a convergence. Perform a convergence procedure on your TV, and if the
problem recurs within a few days/weeks, then your TV's 'convergence
amplifier' board (aka "convergence amp board") is starting to fail.
This board may fail completely, in which case, your convergence procedure will fail to improve the picture.
A "convergence procedure" can be performed entirely by just using the appropriate setup menu option and your remote control.
board may partially fail, in which case your convergence procedure will
properly converge the Red, Blue, Green colors on just part of the
screen, whereas a properly functioning convergence amp board will allow
complete convergence of the colors across the entire screen.
Your TV's convergence procedure instructions will be found in your TV's Owners Manual.
least one Projection TV manufacturer recommends that the consumer
perform a convergence procedure every 30 days, but most TV owners find
that excessive, and might only do one when (a) there's an evident color
convergence problem in any part of the picture, or (b) once every 3-6
How-to video: www.youtube.com/watch?v=esk4nYZKFcg
how-to instructions: www.ehow.com/how_2034880_perform-convergence--tv.html
cost to you: $zero
If the convergence amp board is bad, cost for a service call would be $300 (USD) plus $100 for a new board plus 50% markup on parts = about $450 (USD)
Cost to order a new board online: about $100 (USD) + shipping + sales tax.
if you can solder/desolder STK's (Power Amplifier Integrated Circuits),
one can repair a convergence amp board for as little as $30 (USD) or so.