The Yoyo (L) has an Auto Power Down (APD) feature. The speaker will power down after 20 minutes if no sound is playing from your TV.
The Yoyo (L) will also power down after 10 minutes of inactivity when using the Bluetooth input. However sometimes, when the audio source level is low (e.g. phone, tablet etc.), the device will register the signal as lower than the APD threshold.
To avoid this please ensure that your mobile device's volume is increased to above 50% or more.