cause :
ⅰ) If TV is connected with Antenna signal, Sound may be small depending on the broadcasting signal type.
ⅱ) If the sound level of the connected external device is set to low, the sound output is also low, regardless of the TV’s sound output level.
ⅰ) Check for abnormality of TV volume with performing TV Sound Test function (Sound check) [Home] → [Advanced Setting] → [Sound] → [Sound Test]