RJR: Indeed, but its hard to tell, as it covered its tracks well aside from the arc area itself.
Ken: What you describe is exactly what I am/was seeing, down to the exact arc site. I have a few more continuity checks to try, and I do have a new board I can try eventually, (once I am confident there are no shorts anywhere else).
Alan: Thank you for the tips, but as I mentioned above, the coupler isn't the problem as it was disconnected very early on in the diagnosis, with no improvement or resolution. The arcing was the same as it was with the coupler connected. Also, I already identified exactly where the arcing was happening (see the image above), and examined the site thoroughly. There just isn't anything there aside from the coupler wire, which was shielded and intact, (and subsequently disconnected as mentioned).
