When you do not see any video on your TV or TV states "No signal, is it on?" check the following:
External Coax Device
1.) Confirm the TV is set to the Antenna TV / Live TV input
2.) Confirm the external device is powered on / has power
3.) Confirm the Coax cable is firmly connected
4.) Confirm the "pin" of both ends of the Coax cable are not bent or damaged
5.) Test with a different cable
6.) Test the external Coax device with another TV, does it work (continue to test 7 if device works)?
7.) Confirm the TV has channel 3 and 4, then test with the TV on channel 3 and 4 for picture / signal
External HDMI Device (Not ARC or Sound Device Related)
1.) Confirm the TV is set to the correct HDMI input
2.) Confirm the external device is powered on / has power
3.) Confirm the HDMI cable is firmly connected
4.) Confirm the "connector" on both ends of the HDMI cable are not bent or damaged
5.) Try a different HDMI Cable
6.) Confirm the external HDMI device works with another TV (continue to test 7 if device works)?
7.) From the Home screen confirm under Settings -> TV input -> HDMI [port name] -> HDMI Mode = (For UHD or better content - "2.0") | (For HD or lower content - "1.4")
Note: If connected device is an Audio / Video Receiver (AVR) confirm the "Monitor out" (ARC out for newer models) of the AVR is connected to the TV and they receiver is set to the correct input.
External RCA Device
1.) Confirm the TV is set to the A\V input
2.) Confirm the external device is powered on / has power
3.) Confirm the RCA connectors are firmly connected to the TV (or 3.5mm to RCA adapter depending on model)
4.) Confirm the "connector" on both ends of the RCA cable are not bent or damaged
5.) Try a different RCA Cable
6.) Confirm the external RCA device works with another TV?