misshapen CRT image

[luminescentsimian]

I'm looking for some wisdom from those who have meddled in the dark arts of CRT repair. I've got an Osborne 1 with a Nuevo 80 column card but the CRT is a little off. It works, but once it gets past mid-screen the CRT seem to rush to finish the frame as evidenced by the small "Insert disk" line and the raster completely stopping only 3/4 of the way down the screen. How does only half of the screen end up distorted? I don't understand the analog witchcraft well enough to guess. I've got schematics and a multimeter but there are so many small caps and resistors on the PCB I don't know where to start poking, or if there's any high voltage on the board I need to worry about.
This picture is with the vertical size pot turned as large as it'll go and the brightness cranked up just enough to see the raster.

Could it be an issue with the source signal? Could it just be the vert size pot going bad? The 12V coming out of the power supply seems steady.

 

[3lectr1c]

I'm by no means an expert, but have you tried the usual suspects for CRT issues, such as replacing the analog board caps? You mentioned that there are many ones, do you mean electrolytics or a different type? I've definitely seen this kind of issue before in videos, but I don't remember the cause, or which ones unfortunately. It's probable that there isn't just one cause for this kind of thing.

And yes, there are many points on the board with high voltage.
1. Don't touch anything with your bare hands while it's plugged in, or when you haven't discharged the tube and big caps on the analog board
2. Don't poke at it with any all metal tools, make sure the handle of your tools aren't made of anything conductive.
3. Wear insulating gloves if you're still nervous around it.

 

[Crutch]

I’m just a Mac guy, but distorted 9” Mac CRT displays are typically fixable by adjusting the little magnetic washers mounted around the periphery of the CRT neck.