This is a segment of a schematic of a Yamaha receiver:
My question is about the 4 diodes in mid screen, 2 pairs, each pair back-to-back.
What purpose do these diodes serve?
The conductor common to all diodes runs to the left and connects to the shield on all low-level RCA output connectors.
The conductor running to the right of the upper pair of diodes serves as ground for some circuitry, as you can see, and is also connected to ground at the bottom edge of the board, center.
Here's where the ground conductor originates (seen at bottom of previous schematic):
The conductor running to the right of the lower pair of diodes runs to the right and connects to a terminal labeled "Earth" (top left corner in the following schematic):
These all serve as ground and/or earth and are connected together though these diodes: 3 conductors (analog ground, earth, output connector shield.
Why the separation via diodes? What purpose do these diodes serve and how?