How do you fix an RCA big screen tv?

How old is it? Matbe replacing the color tubes that connect in the back, they are red, yellow and blue. This might help, I know its true for the slightly older big screens, 42" or bigger. Sounds as though your convergence is mis-aligned Mosty big screens have on screen setup adjustments. That you can do right through your remote control. I would begin to make these following adjustments, before I would even consider replacing any color tubes. Go into the Picture portion, then browse the available options until you find "Convergence". You should see a set of bars, similar to a large cross. Most likely you will see a Red Line and your Blue line are not precisely lined up behind the White cross. Follow the instructions on screen for which buttons to use on your remote control and line the color bars until they are hidden behind the white cross. you may have to align one, then move forward one screen and then align the other. Some set's offer even further adjustments with a series, or whole screen of crosses. (Usually, two more pages) If so, Look them over carefully before moving on to the next. You may find that even just a tip of the hidden color that needs to be adjusted on each or every one. Although sometimes maybe only one cross appears out of alingement. * * * And this is Important * * * Once you've re-aligned the crosshairs of color behind the crosses. Remember to SAVE your work before exiting the convergence section. Otherwise, the picture will not be changed and you'll need to go back and do this all again. In closing, if this does not fix the problem and the lines are still apparent, you may need a service technician to come out to adjust the Dynamic Convergence... They'll tell you if you need new color tubes or if it's maybe only a new convergence box. Good Luck and please get back to us and let us know the outcome, as you may be helping others dealing with the same difficulties.