We are having the same issue with the exact same model number. Did you find a solutuon?
Samsung 65 inch model# un65f6300
I have a 3 year old Samsung tv model # un65f6300.when it is on the top half is normal brightness,but the bottom is darker and flickers.i had Sears come out and the tech said it was the control panel.i have pictures and video need help plz Thanks Bob