So, I tried making the adjustments and there was no meaningful change. I suspect there's either an internal issue somewhere or the blue gun on the CRT has died. My question is, how can I troubleshoot this further?
So I acquired this machine today from Freecycle, and the only issue I can find is it has the typical dead 4.5V clock battery which is easy enough to replace, but there's a yellow tint on the CRT that I can't seem to resolve in software. Pulling the back panel off the machine yields only one disconnected cable (shown) that I don't know what it is for. Is the tube dying, or is there some other cable/connection I can check?