"Phil Allison" wrote in
:


"Geoff"

I took the case off and no difference, your implied
suggestion that a change in magnetic field caused this
matches what I observe, ie no electronic settings change
the waveform, it looks like when someone shoves a magnet
near a crt. I have not removed the tube screen but I have
shaken it and nothing like a magnet bouncing around can be
heard,


** The CRT is a *mesh PDA* type - right ?

There must be a chance the steel mesh has become
magnetised.

Suggest you play around with a small magnet near the tube
face and see what happens.

FYI:

There is a fine steel mesh just behind the face of the tube
that has final acceleration voltage applied to it - if you
de-focus the beam you can usually see the pattern of the
mesh projected onto the phosphor.




... Phil




Links below for pics taken with webcam. Mesh is visible.
I have played around with a magnet, can get trace to wobble
around as expected but it comes back to the same position once
magnet removed. This is true for the unshielded part behind
screen and the conical tube shield. I will try a degausser
once I find or make one

http://i251.photobucket.com/albums/g...01/focus_limit
_ccw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_cw1.jpg

http://i251.photobucket.com/albums/g...01/focus_limit
_ccw2.jpg

http://i251.photobucket.com/albums/g...e101/2215a.jpg

http://i251.photobucket.com/albums/g...e101/2215b.jpg