The collected works of Syllopsium

My O2 is working fine capturing video on the composite input from new devices, but refuses to capture more than one fairly unstable frame each time I plug it in and out of an old computer (an MSX 1 in this case). I note someone else had a similar problem with an Amiga 1200 and a Commodore 64, so I'm guessing this is a more generic issue.

Is it possible to easily fix either the O2, or the home computer, to fix the signal as appropriate? It's a pretty old box (1983) and only outputs RF, Composite and mono audio.