No Sound through component cable- but sound OK through AV cord?

I can hear sound thru the 720- Panasonic Vierra TV when playing media though the AV cords, but not through the component cord. I have tried changing the setup to digital then stereo, but this makes no difference. There is no sound through composite using the supplied sample media ( video or mp3) I do not have an HDMI cable to check if the cable is the issue. I do not have an optical cable. :

Component cables don’t carry audio, only video.  You have to use the A / V cords or optical cable.

I don’t know what setup you got, but just because you don’t have an optical cable you are not forced to use the 3 a/v cables. For any decent TV you should connect the video thru either HDMI or component video (the red/green/blue connectors). The composite video connector (yellow connector of the A/V cables)  is just there for legacy support, and delivers a subpar quality, that many ppl would deem unwatchable these days for anything but newscast. If you have a Panasonic plasma/LCD you really don’t wanna connect it with composite, you should stick to component output, or HDMI if you don’t mind spending a bit extra.

As for audio, if you only have the TV speakers then you can do use the analog stereo output (the red/white connectors in the A/V cables), but again that’s just a marginal connection. If you have an A/V receiver with stereo or surround speakers you really need to hook it up with the optical cable, otherwise you won’t have 5.1 sound.