Here is a quick fix to what I believe is a common Sega Naomi video problem. I've seen this happen on two Naomi motherboards I own, as well as on a Hikaru motherboard. Video looks to be smeared or ghosting, like in the picture below.
I don't know exactly how it happens or why (I'm too lazy to really investigate at this point), but the problem is with the filter board (not the motherboard).
After removing the filter board, turn it over and you'll notice a burned trace just under one of the long connectors. This pin is one leg of an RC network that goes to the VGA port, and then runs under the connector to another set of pins above it.
The fix is simple, jumper the two connectors to bypass the burned trace, and your video will look crisp as new.