Just in case a Samsung TV user trying to get an Apple TV 4 to work (eg with netflix) comes by here, this helped me:
Be careful since this might void your TV's warranty eg. if you manipulate other settings.
1) Put TV in standby and connect the Apple TV
2) To open the Service Menu enter this sequence while TV is off: Info - Menu - Mute - Power
3) Now only use up or down! to navigate to "Advanced" but dont press anything
4) Put in: 0 0 0 0 on the numbers
5) Now only use up or down to navigate to "ADJUST" - hit enter
6) Now only use up or down! to navigate to "HDCP Download" - hit enter
7) Use left/right to put it to "On"
8 ) Now to leave the menu power the tv off (standby) and power back on