Remember, the crazy thing is all one big tuned circuit!
From one end to the other, it's amazing how they got it all working so well, but, it DOES mean it's easy to upset the balance, get one key element out of wack, be it the horizontal frequency, something in the damper area, yoke or convergence area, basically ANYTHING that can mess up resonant frequency of the circuit, then you have a big headache on your hands, and like I mentioned, it may very well include the focus circuit.
