Not a fan of the Samsungs- stopped selling them a while ago- but ton the newer Sony's, after a firmware update, they added an "inactivity timer" that shuts off the TV after a set time. In their menu system, you can change the timing or turn off the "feature". Don't know if Samsung has that, but worth a try. Or bad CEC from the cable/Say box. Turn off all HDMI control features.