Ya the guy I bought this from soldered underneath to make it fit inside a NAOMI. I posted about the video issue I was having with this unit a year ago (https://www.arcade-projects.com/threads/hdmi-naomi-2-video-signal-banding-noise.12991/). This was my first NAOMI. I've gotten 3 additional stock NAOMIs since then because this one was a piece of crap.
Getting back to this one and salvaging it. But trying to figure out what this I/O board is since I don't see any markings on the PCB that identifies it.