Plotter works with old LCD screen but not new LED screen. Why?

[Simi 60]

As the title says.
We have a Seiwa explorer mk3 that is using a tired and dull LCD screen so I upgraded to a new IPS LED screen and it gets nothing.
Screen says check cable plug, that is all.

Seiwa blurb says

Seiwa Explorer MkIII is a controller for CRT or LCD VGA Monitor that allows you to match it with any computer monitor you choose, or a compatible TV, and either run it from an existing GPS or attach an optional smart GPS Antenna (GPD905).

so I guess that explains why but really, why?

Screen is OK as it works great with the laptop running opencpn but I was hoping to get a 2nd new screen for the Seiwa.

Is there anything that can be done or do I simply have to buy a new LCD and have two mismatched screens?