I'm back and don't have good news to report. Replacing the CA3126E chroma processor didn't help at all.
Everything chroma-wise is just as messed up as it ever was.
Near as I can tell, the chroma signal makes it to the processor IC in good shape (see my previous post for an example). I don't know what's happening to it after or during its time in the IC...and I really can't imagine the replacement IC is also bad!
The 3.579545 MHz oscillator's output seems as though it goes onward from the chroma processor to a National Semiconductor LM1886N/LM1889N pair. I believe these two ICs are responsible for delivering the character generator output to the final video mix, which is handled by a couple of GT4123A video mixer ICs from Gennum. (I haven't verified that this is fact the exact signal pathway, it's just an educated guess. The PCB is multi-layer and that makes tracing it more difficult.)
The most recent thing I've done is to replace all of the passive devices around the chroma IC for which I have exact replacements. No change has resulted. I didn't expect it to...this was, admittedly, "shotgunning" and wishful thinking.
I've had no luck finding an owner's manual or service data for this unit, and at this point I think I need one or ideally both to go further (although I have a few ideas I'm going to check out in the near future). If you have some of this information for this unit,
PLEASE contact me!
Otherwise...I'm nearing the point where I feel I've spent more time on this thing than it's worth. (So far what keeps me going is the fact that I really don't want to let this thing "win".)