Hello jstout66,
I have worked on a few Zenith Chroma II's and as you know the main chassis is hand wired so intermittents on the chassis are very unlikely. As time goes by carbon builds up on things like module connections and tuner contacts causing intermittents. One thing that has worked well for me is to take a paper towel and wet it with tuner cleaner(make sure it is safe for plastic) and with the module unplugged run it over all the male module contacts. Then take and spray a little cleaner into the female contacts of the module. Sometimes the little fingers inside the female contacts need to be pushed in just a little to return enough tension so they make a solid connection. Mom had a Chroma II and I solved a few intermittent problems with it that way. One other thing to check would be the lytics on the module with luminance/sync. Good luck and let us know how things go.

Jeff