the apple..

[rca2000]

It is possible that part of the 18 volt line is scan derived, and so, without the horizontal running, you may NOT see the full 18 volts.

On each side of my Crt, there is photodiode assembley, that picks up the index phospor, to tell the index circuitry where the beam is. In the manual, it says something to the nature, that the index phospor(the green glow at the back of the screen) starts several lines before the view phospor. this is so the circuitry knows where the beam begins, and ends. I will have to go back into my manual to find out more. It does describe the beam index principle, using photo-electrical guidance.