When you connect the accessory device to the AV1 input of the TV using either component video cables (YPbPr) or composite video cable (VIDEO IN), you must connect the audio output from the accessory device to the 'AV1 AUDIO IN L R' of the TV using the RCA audio cables (Red and White).
If the connection is good:
Check to ensure that the AV1 audio source in the TV on-screen menu is selected to AV1.
Make sure that the volume on the TV and on the accessory device is set at an audible level and also that the sound hasn't been muted.