A few thoughts:
Obviously you don't need an ion trap magnet. Since you have a dot when the scanning stops, which indicates the electron beam is centered, hitting the screen. Without video, you should still have a full screen raster, so I would bet that the crt has low emission.. Without scanning, the electron beam is concentrated enough to make a dot, but when scanning it is spread out so thinly over the screen that it is not strong enough, (low emission), to cause the phosphors to glow like it does when it is concentrated in one spot. You might get a tube brightener from ebay and try it, or get a crt checker to check and if necessary rejuvenate the tube. After you get a raster, you can worry about video. Since you have a scope, you could check the video detector output and see if you have a signal there. You may not, since you don't have sound either. If not then the video and/or if/rf section would need to be checked. Since you checked voltages and found them to be correct, then I doubt that the crt is biased to cutoff, but you might recheck the grid to cathode voltage on the crt.
Donald
PS:
You can copy and paste this article on crt rejuvenation: file:///E:/Documents%20updated/Antique%20Radios/CRT's/crt_rej.htm