Have a hisense 50 intv have sound and pic go out after 4 mins of use . Try unplug it power reset thing and every thing else I can think of .

Fix my TV and gave me a 90 day warranty cheaper than buying new one

Most likely the LED backlights are failing but it could also be a bad main board or power supply. At 50" size in a low end brand like Hisense cost of repair and cost to replace will not be that far apart. I can fix it for you but probably not at a price that is much less than buying a new one. More bad news - I am at least 3 or 4 weeks behind, if you brought it in today it would be at least that long before I could call you with an estimate.