Weird Lisa CRT reverse pincushioning

[wottle]

I was looking at FB Marketplace for anything interesting and came across a Lisa. The price is too high, but what really struck me is the video showing it powered on and working. The CRT seems to have an issue where the viewable area on the screen is limited to a circle (cut off at the top and bottom). It's not pincushioning (at lease I don't think it is) because it seems to be a perfect circle.

Anyone seen anything like this before? Is it just the worse form of reverse pincushioning ever on a CRT?

 

[warmech]

That's... weird. And not normally how pin-cushioning should look. Poorly adjusted pin-cushioning should yield an image whose contents are warped proportionally to the pincushion (think: how light warping around a black hole looks). See this post over on arcadecontrols. This image looks like it's just... masked into a circle. There's no distortion, it's just cut off. It's not externally masked, so that's on the CRT phosphors themselves.

I am so confused by this image.

EDIT: Sorry, this wasn't meant to sound condescending - this was just me thinking out loud. I genuinely have no idea what's going on here, lol. You're completely correct, though, there's no way that's pin-cushioning!

 

[stepleton]

+1 --- I've never seen anything like this before.

The raster itself looks fairly linear (so not pincushioning or similar distortion) but the picture (or the part of it we can see) is bigger than it should be, almost "zoomed in". Meanwhile the extreme "vignetting" almost looks like a shadow --- and I tend to suspect that it's probably just that, a physical thing that's blocking the electron beam. My best guess is that the trouble lies in the CRT itself, and that one of those metal bits inside the CRT neck that's involved in shaping and focusing the beam has become dislodged.

Again that's a guess; I really don't know but would love to find out. We'll probably never get to inspect this Lisa itself, but maybe ask on a forum with a lot of CRT or TV repair people?