There is a headphones volume setting in the TV menu, which is used to adjust the headphones volume independent of the volume control for the TV loudspeaker.
If the headphones volume is set to minimum, you will not be able to hear sound from the headphones.
Before you proceed to check the headphones volume, be sure that you have connected the headphones to the [Headphone] input at the rear of the TV. Do Not connect the headphones to the ‘SERV.U’ connection, which is for service purposes only.
To adjust the headphones volume, do the following:
TV's rear connectors