Samsung Q800T Series E-Manual page 149

The problem
The volume of the external device
cannot be adjusted.
I want to turn off and on the TV
and audio device at the same
time.
Check the cable connection between the TV and the external device.
When connecting an external speaker such as home theater via HDMI, make sure it is
connected to the HDMI (eARC) port on the TV. Make sure that the
General External Device Manager
When you connect the Samsung Soundbar to the TV via Bluetooth, the power turns off
and on together. It may not be supported depending on the Samsung Soundbar
model.
When you connect an audio device that supports HDMI eARC to the HDMI (eARC) port
on the TV, the power turns off and on together.
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Try this!
Anynet+ (HDMI-CEC)
Settings
is active on your TV.