To diagnose why your Smart TV is not connecting to the soundbar, follow these steps:

1. Verify your hardware connections – Ensure that all cables are securely plugged into corresponding ports and that HDMI cables are compatible with your TV and soundbar.
2. Verify soundbar volume is set to a reasonable level – Make sure the soundbar is set to a good level in order to receive adequate sound output.
3. Double-check external device outputs – Check to see that your external device is outputting the sound to the correct source.
4. Make sure the soundbar is powered on – Test this by pressing the power button on the soundbar, or by using the volume knob or remote control.
5. Reset the soundbar and TV – Unplug both the power cable from the soundbar and the TV and plug them back in.