Panasonic AV-HSB300G Operating Instructions Manual page 6

Mounting
3 Remove the upper panel cover.
Upper panel cover
4 Remove the  screws (B), and remove the blank panel.
Blank panel
Screws (B)
5 Remove the 3 screws (C) and  cable clamp.
Screws (C)
Cable clamp
6 Insert the HD analog board from the inside of the rear panel, and insert it along the guide rail for the connector.
(Insert it securely and completely.)
HD analog board
Connector
5 (E)