So I have found a remote around the house that is compatible and have verified that the TX mode is set to HDMI. Also tried fiddling with all the other options but nothing affected the sound. I tried re-flashing 0.78a, and also downgrading to 0.77a. Neither of which had any effect. I’ve done a visual inspection of the board and everything looks alright. And I’ve swapped the OSSC out for my cheapo scaler to verify that the console, tv and cables are all functional, which they seem to be.
Any ideas for next steps? I have an old analog oscilloscope and an fpga board I can use as a logic analyzer. But I am not very skilled with those tools yet.