Yet another Zenith To identify

[jstout66]

The thing that can be a pain in the ass on a Chromacolor 2 chassis is the modules. Manufactures loved those upright chassis with plug in modules during that era, and as they've aged have become problematic. I would say the XL100 is the worse.
As for your Zenith, carefully remove each module one at a time, and firmly plug them back in. Loose or dirty connections cause about 90% of the problems in those. For your brightness contrast issue, I would say you have a bad or loose video module.
If there is any module you need or want to try, let me know. I have a TON of NOS CC2 modules. I can't guarantee they're good tho. You never know how the caps have held up even being unused for 35+ years.
I hated that tuner and not sure I'll have one. It's on a module as well, and we replaced a ton of them in the 80's. If yours locks in with AFC on you should be fine. You really only need channel 3 or 4 anyway.....
I would have thought cleaning the volume control would have helped. What cleaner did you use?

[zeno]

Check the long resistor packages on the 9-88 & 9-89 modules.
They get cold joints. May be flickering & brite problem.
Be shure the chromatic switch isnt noisy by wiggling it.

Cant see the tuner (s) so pull it/them out. Resolder under the
connectors. Also there is usually a tuner control module,
check the PC there. Clean AFC switch. The tuning pots sometimes
get noisy too.

Audio is probably a bad control especially if its a slider. Try
other cleaners. WD40 can work miracles.

73 Zeno