Blank external screen, games only on built-in LCD on laptop

[PsyQ]

I'm trying GroovyArcade on an old IBM T42 with a Radeon Mobility 9800. Installation went well and I even had a picture on the external screen via a VGA to RGB SCART cable. The screen is an old Phillips RGB monitor like they used to sell with Amigas and C64s. However, when I started AdvanceMENU, either from the live CD or from a HD-installed GrovvyArcade, the picture is only on the internal screen. I've selected VGA-1 as output, though, and a generic 15 khz screen configuration. I've also tried PAL with the same results.

Also, when starting LXDE the only resolution I get for the external screen is 640x480 (interlaced), which cuts off bits of my desktop.

Did something go wrong with the modelines for the external screen? Is this configuration even supposed to work or is the lappy simply too old?

[Calamity]

Hi PsyQ,

This is a known problem that unfortunately makes Groovy Arcade not suitable for laptops. The reason is that Groovy Arcade can only work on the primary display. Laptops always map their own LCD screen as the primary display, so there's nothing we can do.

Ideally you should be able to launch the frontend with a proper resolution on the LCD screen by using the SVGA boot option, and then make GroovyMAME point to the VGA output and use 15 kHz on there. The problem is I have never managed to get this working. I believe the problem had to do with the normal build of GM using SDL 1.2. When tested a build using SDL 2.0 it did behave different but still didn't work. Some people say it should be just a matter of configuring xorg.conf properly, but I've never seen anyone that got this working.