It's not your TV
I had the same problem.. Then I rememberd I had changed my HDMI cable a week prior. I put in another one and I did do one turn off, then I unplugged my sound system from the back of the TV ( it's an LG sound bar) . My Bravia has been going now for 2 hours and no shut off yet. Not sure which things made it work, but I did turn turn off my cable to reset it as well. I will add my surround back and see what happens. The point is, get rid of anything plugged in or out of the TV because it can be causeing a interrupted power loop that sets off a trigger standby on the TV, hope this helps!