I usually have my MiSTer going to a 90s CRT directly via VGA to Scart.
But today, I wanted to try an older set (from the UK), and plugged the Scart into the back of the VHS player, with RF out to the TV, but the display is almost black, only very faintly showing signs of anything coming through (my Nintento Wii works fine doing it this way).
But what settings do I need on the MiSTer in order to get it to work?