I forgot to mention that this monitor has a DB9 video input connector
at the back.
But it is for NTSC/RGB as far as I can tell, not for CGA or VGA.

The connector pinout is:

pin 1: ground
pin 3,4,5: RGB inputs
pin 8: composite input (video + sync)
other pins not connected inside.

Thanks and Cheers,
- Sylvain