The good thing about this board, is as far as I can tell there are no other traces on the other side of the board. (there are some caps in the way)
I think you are right though – something just isn’t hooked up/bridged. The face that composite and s-video work means it can output video/Sync
See below for a link – this is what i rigged up for testing I”ll clean it up a bit better once i get it working. (also the resistor is in the electrical tape)
I checked the continuity, and the traces are cut properly. The Yellow wire is the sync on composite signal and it runs all the way to the yellow RCA without issue. (even after this mod the audio and other video outputs work)
The black wire (CSync) I can trace right from the start (from the video encoder) right to the AV Port. Not sure what pin it’s supposed to go through, but I can check when I get home if someone can confirm.
Also I reflowed the solder on the AV out, just in case that was it.