Kevin F, That resistor just outside your circle is NOT factory. I’ve attached an image of that area on another Genesis Model 1 board.
There were a lot of mods done to these over the years, and this is one of them. Unfortunately, there’s really only one way to figure out which mod this is, and that’s to ask someone heavily into Sega modding. I’m not one of those, so my solution would be to traverse the darkest and weirdest corners of the modding interwebs
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