I am running the Debian distribution on a Manx PC104 embedded board. The board has a normal VGA video output that I have connected to a monitor and this works fine.

It also has an LVDS Panel Display output which is reported to be logically the same as the VGA. When I connect an LCD panel to this port here's what happens.

1) I see the Linux Penquin logo and the initial start text on both the VGA and LCD panel. So the hardware interface is working.

2) The system switches to a default wallpaper background. (I assume it has entered some graphics processing instead of text.) I continue to see the upper left quadrant of the picture on the LCD while the full screen is display on the VGA

3. Both screens blank except for a waiting icon on the VGA.

4 The VGA display goes to the final desktop with a Task bar on the bottom and, as it turns out, the browser covering most of screen. However the panel still remains blank.

5. When I shutdown the system. VGA graphics is replaced by the console text showing the final shutdown process. At this point, the panel comes alive again and shows a quadrant of the VGA screen.

My questions are:

1. How do I get the panel to remain active through the main graphics portion?

2. How do I adjust the system so the the panel show the entire display?

3. In short, how do I get the panel to mimic the VGA?

You want to mimic iow have 2 identical screens show up across both monitors? Or "extended" view with 1 monitor on the left, for instance, and the other on the right?

Have you tried using xrandr?

$ xrandr --output LVDS --below VGA

Will display the X output of LVDS "geographically below" the VGA X output. Use "xrandr --help" or "man xrandr" for more settings.
If the chip is nVidia, you could probably do this with the proprietary driver as well.

Not displaying the full screen or blanking out on LCDs usually is caused by wrong settings for resolution and/or refresh rate. Try to set the correct settings for the LCD.

My problem was caused by a faulty setting in the CMOS EEPROM. The LCD was not enabled which is why it worked only part of the time. It certainly wasn't enabled with a resolution corresponding to the actual LCD,hence the truncated display.