Hi,
Here’s a link to the [https://www.manualslib.com/manual/804947/Pioneer-Vsx-821-K.html#manual|service manual] for your receiver.
It has all the information that you need to repair the receiver.
The main power fuse is located on the [https://www.manualslib.com/manual/804947/Pioneer-Vsx-821-K.html?page=10#manual|standby assembly]