The one with the decoder and RAM on it. While these are no TV repair forums your TV repair person will likely change out the big board in the set.
I have a Sony Bravia TV (model KDL-46W4100) and recently it started having these colored squares and distortions in the picture. It only changes the color of the area, the picture coming from the movie/video game/cable is fine. I cant find the same problem like this on my search of the internet but maybe someone has seen or experienced this and has some advice on how to fix it.