Matthew SparbyFor nearly 5 years, I've been trying to figure out what this adapter is supposed to connect to. It's still a mystery. Someday, the right person is going to see this post and they'll finally solve this puzzle.
Elias Mårtenson@Cloudscout that looks like an Atari ST video connector.
@Cloudscout the ST connector is described on this page. https://info-coach.fr/atari/hardware/interfaces.php