firstly, disconnect your aerial from the vcr, so you just have the
video connected by coax to the tv. Then adjust the tv fine tuning, see
if that helps, it may have drifted.
If the colour appears, that may be all the is to it; if when you
reconnect the aerial the pic is b&w, you need to adjust the UHF output
on the vcr (i think this model has a small screw at rear to adjust ch
range: UHF 32-39

of course the modulator could be bad or its supply voltage unstable
due to bad PSU caps, but lets not get ahead of ourselves. let us know
how you get on

Thank you. I tried to fine-tune while aerial was disconnected and the VCR
was playing a cassette, but no help: the pic just went worse. So apparently
the TV tuning is ok.

Otherwise the VCR works fine and the (black-and-white) pic is very good.

M