Picture tube arcing

[Dreamsbeard]

I finally decided to start working on my 84 Hitachi console to see if I could get something out of the old girl. The set had a dim picture, so I decided to test it with my B&K 470. Sure enough, the red gun was low (still in the good area, but lower than the green and the blue), so I decided to go ahead and "clean and balance " it. The result was not satisfactory so I decided to go for a full rejuvnation, and that worked quite well.

After that I went to ajust the grayscale/focus/convegence. The brightness was still low so I went to the flyback to adjust the "screen" and "focus" control, and as soon as I touched those two pots the neck of the tube started to arc like crazy, and of course that caused the picture to get funky or to not display at all. At that point I decided not to meddle with it anymore. So I unpluged the set.

So, I wanted to ask, what might cause this? Could bad flyback pots cause arcing in the neck of the tube? Could this damage the tube? Before repluging the set for convergence I did check for short with the tester and there was none...

Thanks!