Re: 475 With a bowed display. . . .Ideas?


Chuck Harris
 

I don't think so, and here is why:

When the scope is exposed to a strong magnet,
the field lines extend in loops from N to S poles.
When those flux lines confront a magnetizable metal,
they are distorted and concentrated into that metal,
making for truly weird looking flux arrangements.

On screen, such magnetizations of the mumetal
shield, which really is the only magnetizable material
anywhere near the CRT will make beam deflections in
small areas. This typically shows up as a kink
somewhere on the screen, near one edge.

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A power supply regulation failure could cause a progressive
pinch of the screen width making a "keystone" shape.

-Chuck Harris

Keith wrote:

Just thinking out loud here - if a scope sat on a bench (or in storage) in one position for a long time near some relatively powerful fixed nearby magnetic field, (like a big permanent magnet loudspeaker assembly, etc.) I suppose it is possible for some nearby magnetic anomaly like that to gradually induce a very specific magnetism somewhere, leading to visible misalignment? Such an unwanted magnetic influence could produce a very specific distortion and it would seem reasonable for such an influence to be most obvious on traces out at the edges of the CRT.

Maybe you could try degaussing the shield around the CRT? You can borrow my degaussing tool if you want. Sometimes it is the simple stuff. PIA to remove the shield and separate from the CRT, but that is probably the safest way to do it. Of course you would first have to remove those steering magnets like someone mentioned, or the degaussing tool would ruin them. Of course this means even more fiddling, but hey...that’s why we do this hobby, right?

Also, maybe the shield has been damaged by some mishandling in the past? Tek says, and I quote

“CAUTION This Mumetal shield has been carefully annealed after fabrication. Any shock may destroy its magnetic shielding characteristics”

So obviously it is possible for them to go bonkers. Just a thought...

Cheers,
CBG



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