Video turns off after about 10 seconds

When connected to input(YouTube tv via Roku Streaming Stick+), about ten seconds after set is turned on, it goes “dead,” I.e., no sound or picture and no response to remote buttons except for Power- which when pressed powers set off. When input is removed, set powers on and stays on, displaying menus and inputs. When built-in self-diagnosis of video and sound is activated, sound checks out okay. But when video check is made, internally provided picture displays, flickers slightly, dims, and tv becomes “dead” as above.