Check the speaker cables to make sure they're connected the right way. Make sure there isn't any physical damage to the cables that could short them out. If the cable polarities are right, there's a chance it will have to go into a repair shop as a circuit inside of it has failed or been damaged.
You'll need the manual for the SC HT800V. On page 2, there's a parts list table that shows the SA HT800V is the amplifier part of the SC HT800V system. Here's a download link (the cover page of the manual says it's for the SC HT800V and two other models):
Panasonic SAHT800V user manual Operating Instructions
You can't record a CD that is playing on the Panasonic SC-HC20DB to the iPod. However, if you rip the CD and put the contents of the CD on your compatible iPod, you can play the resulting audio files on the Panasonic SC-HC20DB. The list of compatible iPods and iPhones is available in the manual, see https://www.manualslib.com/manual/647714/Panasonic-Sc-Hc20db.html?page=12#manual for a copy.
I hope this helps. Note: the SC-HC20DB only plays CD-DA and MP3s on CDs. I'm not sure if the restriction applies to audio files from the iPod.
Cindy Wells
I have posted the page in the service manual for this issue. It is not something that a person with no electronics experience can fix. It requires product knowledge of integrated circuits and use of electronic meters and the ability to solder. https://www.manualslib.com/manual/768347/Panasonic-Sa-Akx74lm-K.html?page=29
