[Jeffhs]

I recall reading in a very old (circa 1950s) television repair manual that misadjustment of the ion trap can also cause ion burns, some of which were very severe. The manual had a picture of a CRT screen that had suffered a very large, circular ion burn, and also a photograph of another screen that had an ion burn in the shape of the letter X. The manual stated that the round, large ion burn was more common in round CRTs, while the X-shaped burn appeared mostly in rectangular tubes.

The bright white line that appears across the CRT screen when vertical deflection is lost will burn a line directly across the middle of the tube, if the brightness isn't turned down to zero--fast. However, I have often wondered about the line that shows on a color CRT when the service switch is on (in the service position), which of course kills the vertical sweep. Is that not a potential danger to the CRT phosphors? I would think it would be. The only way I can imagine this not to be a danger to the screen is if the brightness level of the setup line is very low (just bright enough to see), and there is no way to increase or decrease the brightness of that line with the TV's own brightness control.