The pixels on the screen will be identified by addresses for row and column - from what you say there's a problem with the column addressing - it may be a problem with a poor joint or an issue with an electronic component where a signal is sometimes being "seen" and sometimes below the threshold of being recognised - when that sort of thing happens it's sometimes associated with the internal temperature - heat changing the way the chips work.
You would be very lucky to resolve this problem yourself - if it were my set I might consider arranging to have a fan blow cooling air into the back - just to see if it changed the nature of the fault in any way - but I suspect it will need to visit the TV doctor.
Good luck...
I am not a TV engineer - all this is pure guesswork.
Peccavi, May 2013
