Yeah, but when they came and replaced the motherboard, and then they turned on the tv, was it happening then still? Or is this something that developes after a few days? Question here being, that if this is some issue in your place, like the wiring in your wall outlet or presence of some electrical device nearby that's interfering with it, lines will be happening immediately after repair. If this is some issue with the tv itself, it might be working for a day or two after repair guys leave, and then start appearing again.