TCL 6-Series Google TV R646 has picture but no sound

The checks in more detail

If sound returns, the problem is the external device or its connection. A Bluetooth headset that remembers the TV can take over when it is switched on nearby, so turn it off. For a soundbar on HDMI eARC, use the port marked eARC, a good cable and turn on HDMI-CEC, called Control Other Devices in some versions, in the TV's settings. Set the Digital Sound Output to PCM or Auto, since a soundbar that cannot decode what the TV passes through will be silent. Restart the TV and the soundbar by unplugging them for a minute.

If sound is missing from a single source or app, check that source's audio setting, for example a surround format your equipment cannot play, and try another app. Google TV apps have their own audio settings. Update the TV in Settings, System, About, System update. Clear the cache of the app if only one is silent. A factory reset, in Settings, System, Reset, clears sound settings but erases your accounts, so use it as a last step. If sound is silent on every source with TV speakers selected and headphones work, the speakers or the audio board may have failed. Contact TCL with the model number and serial number, and do not open the TV.

Keep the volume moderate when testing. Google TV keeps a separate volume for each output, so a TV that shows the volume bar at a high level while Bluetooth earbuds are connected may be sending all the sound to them. Check the output name on the volume bar and in the settings. If the TV was moved or a cable was changed, run the sound setup again. A software bug in the Google TV home screen can also mute the audio focus; restarting the TV from the settings menu, not just by the remote, clears it. Try playing a different app and then a USB video to compare.