Increase the VOLUME to check.
Check that the TV is not muted, press the MUTE button on the remote control.
Check that the earphones are not connected.
When no signal is detected, the TV automatically switches off the sound. This is correct and does not indicate a malfunction.
If you are using Red and White Audio cables make sure they are secure.
If you are using SPDIF out connection with external audio equipment, it will only have output with digital channels.