Double lettering on red when in 1080i good picture in 480p

Phillips 55PP9352 rear projection tv. Picture is great when cable receiver is in 480p and when its set to 1080i the picture gets blury with double lettering. The cable man pulled up a screen with red and green + that didn't line up and another screen with blue + that looked fine. Called tv repair shops and one told me I needed a convergence and it would cost about $300. Is this something I can fix myself without causing more damage or is worth the $300 to get it fixed?