The coco1 has composite video available inside the unit that is fed into the rf modulator. It can be extracted with a small circuit, but the one I have tried throws the colors off. The coco2 has half the video circuit inside the modulator and has no composite available in the unit at all without adding a much more complex circuit.
The 3 has composite only.
As far as I know svideo is nowhere to be found because of the Motorola 6847 video chip, which was paired with the mc1372p to get the video output, and the mc1372p could be configured as rf or composite output according the the circuit.
The 3 uses a different video chip call a Gimie, it has the following.
Output to a composite video monitor or analog RGB monitor, in addition to the CoCo 1 and 2's TV output. This did much to improve the clarity of its output.
I've been trying for the last year or so to get good composite out of a coco 1 or 2, and I was finally given a coco2 that had the above circuit already installed. It works nearly as good as the output from my coco 3's.
Later,
dabone