Its been a Iong time since I fired up an 800XL (PAL). I tried it first using the RF Out which produces the normal blue background booted in basic on a TV.
I scored a Mercury CRT Monitor and bought a Monitor to SCART cable for the XL. When fired up the image is completely dark and dim. Barely visible. I then discovered a RGB/STATUS button on the back of the mercury that resulted in the image appearing, but B&W when booted.
Is this a cable fault or is it possible the monitor is NTSC? It shouldnt be, but its doesnt state what it is.

Cheers!