A photo of the display on an old Toshiba 205CDS is here.
http://carnot.yi.org/Satellite205CDS.jpg

An external monitor connected to the machine is illustrated here.
http://carnot.yi.org/SatelliteExternalMonitor.jpg

From that I conclude the problem is in the video
adapter rather than the laptop screen or monitor.

This is approximately how the display should appear.
http://carnot.yi.org/SatelliteModel.jpg

Testing the video adapter isn't as easy as swapping
a card in a desktop machine. Any ideas for a repair?

Thanks, ... Peter E.