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
Bad news the main power amp has failed.
The good news is that the service manual is online and it's free.
You will need to read the manual and find IC500, which it says is an RSN3502C.
Panasonic SA AK22 Service Manual Page 126