I can almost guarantee that your CRT has lost vacuum… that sounds like high-voltage arcing somewhere. I had the exact same issue with a Macintosh SE that was dropped… if you remove the board off the end of the CRT, there’s a glass “nipple” that is where the tube is vacuum sealed - this goes right into the CRT socket and is easily broken, especially when dropped. Once that happens, the tube loses it’s vacuum and is toast, there’s no way to fix it without replacing the CRT - fortunately there’s LOTS of them out there and the job is very easy to do, less than one hour I’d say.