well the LC550 board doesnt have them. so the first assumption that comes to mind is maybe they are pumping a higher voltage in the LC550 on that supply line becuase the LC runs at 640x480 and the color classic does not. and the transformer mods that are floating around to boost the color classic res, may only be as simple as removing these zeners. LOL. well, anyway, either that or fry. hehehehe. (my analog board is screwed anyway, might as well try. )

and as far as parallel zeners, yeap your right because even though on paper they might be ideally matched, but thats only under ideal conditions. there are losses that might be slightly different between the two and that didnt work so well. hehe.

if it were me, i would use a bigger dumping resistor so the zeners wouldnt heat up as much, and leave the longest leads as possible on the zener to help disipate the heat.