Ferrari F355 Challenge Twin for DEMUL has 2 screens, can I help?

each so called "twin" arcade cabinet have one screen only.
but two or more such cabinets can be linked via (unemulated) network.

In game, show screen on the Multiboard Slave.

as it supposed to be, this is how this game works.
it have one "main" motherboard which handle game logic, inputs, produce sound and music but does not show anything, its video output is not connected.
plus one more "Multiboard Slave" mobo in "twin" setup, or 3 more in DLX setup, which draw and show game onscreen(s).

so, thats wrong ?

If you FullScreen, has the black screen.

don't use fullscreen then