Mobility RADEON 9000 : s-video output tapes as black and white SOMETIMES

I've got a Dell 600m laptop with A12 bios and standard ATi Mobility RADEON
9000.

TV_out via s-video displays just fine on VCR (and thru receiver too). Yet when
I tape to VHS the first recordings are fine; in colour. When I hit record
again - the recordings go to black and white; but the image on the screen is
still full colour. Happens with Windows XP desktop and also when viewing
movies. Any ideas? Output is set to PAL which is correct for Australia.

Same result if I change to a different s-video input on the VCR or change
cables. VCR is a JVC HR-S5990AM which has s-video support.

Thanks
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David S
Melbourne Australia