What I meant by "one color" was that the convergence control for all of the colors would be affected, not just for one color. Your problem is that only one of the controls fails to do anything. Hence, it's extremely unlikely for it to be a "grid voltage" problem, "bro."

Regrettably, I don't have any schematics handy. But again, you have a 550 that works. I recommend again the steps I mentioned in the previous post (measuring the voltage adjustment range of the working vs. nonworking convergence control). Also, perform a careful comparison of the crt pin voltages of your working 550 and not-quite-working CC. That should be sufficient to localize the problem. From that point on, you should be able to pinpoint the defective component. And again, the value of a careful visual inspection is not to be underestimated. This includes a look at the crt socket pins and connections.

Good luck. I'm sure you'll figure it out.