Hey dartman912
1. Press the HOME button, then select [Settings] at the bottom of the screen using the left/right buttons.
2. Select [Sound] using the up/down buttons, then press the "OK" button (It looks like a dot with 4 dots around it).
3. Select [Headphone Speaker Link] using the up/down buttons, then press the "OK" button.
4. Select [Speakers Off] or [Speakers On] using the up/down buttons, then press the "OK" button.
5. Select [Speakers Off] to not output sound from the TV’s internal speakers when you connect headphones to the TV. Select [Speakers On] to output sound from both the TV’s internal speakers and headphones.
Note that you need the original remote to do this, hope it helps hey! If it does not work let me know so we can make another plan.