Tek 465B Oscilloscope Strange Spot on Screen Moveable With Magnet

[cjs2pc]

Hi guys,

I recently purchased a Tek 465B on eBay and have a weird display issue.

There is a strange dead spot on my display always in the same position. It is a round circle where the trace is blanked out. At first I thought something had happened to the phosphor coating at that location and it was burned out.

http://imgur.com/a/xVD8U

However, when I place a magnet near the screen, the trace line is distorted as expected, but interestingly the dead spot moves with the trace, so it seems like this is an issue with the beam generation not the phosphor.

Has anyone seen something odd like this before?

[StillTrying]

I think it has to be a particle stuck on the CRT's post deflection mesh, but I don't know the solution, it may be a case of gently tapping the CRT in the right place - or not.

[tggzzz]

I think it has to be a particle stuck on the CRT's post deflection mesh, but I don't know the solution, it may be a case of gently tapping the CRT in the right place - or not.

I agree.

Note that the mesh is very fragile, and might be damaged by a strong magnetic field. If the CRT is disassembled, even breathing on the mesh is sufficient to warp it.