The IEC serial bus on the other hand is handled by the CPU it seems. There is an inverter and some ferrite beads in there, and that’s it. A few pullup resistors as well, but nowhere does the bus cross paths with the audio signal. At least in the schematics.
I traced the audio signal through the whole schematic and this double diode bodge is super sus. The right one shouldn’t be there at all and connects to the IEC port. It feeds directly into the audio circuit. The left one should be there, but wired to the OTHER side of the resistor. What HAPPENED to this board???
@root42 well, at least the electrolytics seem to be Audio Grade™, as they're labelled ''Grand Sonic'' 😜