The Apple Multiple Scan Displays cannot show a video image using a 512x384 resolution. When a signal using this resolution is sent to a Multiple Scan Display, the image and the raster signals are cutoff and the LED displays an error condition.
To correct this problem, use the reset button on the computer, or hold down the Control, Command, and Power-on keys on the keyboard to restart the computer.
After restarting, the video returns to either the television, or the monitor. If the video is on the television, do the following to get the video on the Multiple Scan Display:
1) Open the Monitors control panel
2) Click on the Options button
3) If the "Upon Restart Display Video on Television" checkbox is
selected, click the checkbox to turn off this option.
4) Click the "Display Video on RGB Monitor" checkbox
5) Click the "OK" button
6) Close the Monitors Control Panel
7) Restart your Macintosh Computer.
Support Information Services