Experienced? I've been repairing TVs for over 50 years. And yes, I've come across this problem, but you said you disconnected ribbons from the lcd to the main board. Do you mean T-con to main? If so, try same with ribbons T-con to lcd panel. If you get the same situation, then one half of the panel is faulty and dragging the data down. Bruce
Sorry, I misread that - no T-con on the TV, built into the main - so only one pair of ribbons. I still say it's the display panel.