Fat trace on tek2213 but it's weird

[tkamiya]

I have a really odd symptom on Tek2213.  Say I have a trace going.  Brightness is set at appropriate and usual level.  Focus is set to a fine point.  If I scan at low speed, it looks all ok.  If I speed it up, it gets REALLY FAT, like 4 mm thick trace.  At this point, I can re-adjust focus and get a fine point again.  If I go even faster, it focuses again.  Vertical is set to 1V or so.

I've seen traces get dim and fat at high speed but I've never seen a symptom like this.

What is this??

[David Hess]

I think the 2213/2215 have an automatic focus circuit which is suppose to adjust the focus with intensity changes.  It may not be working correctly.