> Thank you for the answer.
> Unfortunately I've bought the st-v with no cartridge, so I can't tell if it was
> supposed to be used by a game or some kind of application.
> Anyhow the only relevant things I can tell are:
> 0) This daughter board is an original Sega board.
> 1) The main board dip shitches have the following configuration:
> JP4 = 3-2
> JP3 = 3-2
> JP2 = 2-1
> JP1 = 3-2
> which is quite unusual according to the st-v service manual.

This is the hardware country setting I think now your board is hardware setting for USA (i need to check).
just like the saturn bios can be JP/USA/EURO and the board can be set to different region. some game will check bios region, other (sfish2 on stv side) will check board region.

> 2) Once plugged in a cabinet, the board complain for a missing cartridge (I've
> no games at the moment to play with) and there is no extra test menu entry in
> service mode (i.e. st-v standard japanese bios, so it is meant to be used by
> some kind of game/application)
>
> I'm sorry, but I'm not able at this time to tell where this board originally
> cames from. I'm investigating about it.

That board came from a photo machine, the input is from a camera and the output goes to a priner, like snk neoprint that use a mod neogeo board.

ANY