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

Michael W. Lynch

On Sat, Aug 8, 2020 at 08:22 AM, Chuck Harris wrote:

Typically, when a proper application of the Geometry,
Focus, Astigmatism, Trace Rotation, and other affiliated
adjustments results in a screen that just doesn't look
as pretty as we would like, it means that there has been
an outside physical influence on the CRT (READ: OOPS! BANG!
$%^! & #!!*^! Why Me???)
No signs of major trauma, but this is still a possibility. What confuses me in this regard is the fact the the unfocused spot on the CRT is beautiful and round, one of the best I have ever seen.

The Mumetal shield can get bent, or magnetized.
Not bent, but magnetized? VERY POSSIBLE. I am curious how such magnetization can occur as this issue has come up in other threads as well?

One of the steering magnets (held with Scotch tape) can fall off
of the CRT neck, causing the beam to partially strike one
many internal shield electrodes that looks like a hole in
a plate of metal.
I can look at this when I pull the CRT. Would this not distort the unfocused spot (mentioned above) somehow?

Or, it can be that we are much more nit-picky than tektronix
was originally.
I'm just not that picky. I do not think I am asking too much for the markers to be vertical and consistent across the entire viewing area (or at least within one minor division). If it was just one minor division of deviation, I could live with this, but the outermost vertical markers are about 6 minor divisions "leaned in" at the top of the marker. It is almost like looking through a "fisheye" lens.

If you carefully read the specifications in the manual, you
will often find that we have been spoiled rotten by all of
the CRTs we get that are much better than the specifications
say they could be...
I totally agree. The CRT is one of those items that is a source of constant amazement for me. How they work and withstand decades of use and many times abuse. They are a marvel.

Bottom Line, sounds like I need to pull the CRT and inspect it for obvious damage. I can try another "known good" CRT, as I have one or two that produce very good and well aligned traces in other machines.
if a "Good CRT" shows the same symptoms in this chassis, then I need to look elsewhere.

I was thinking that I had missed some other related adjustment? I guess not?

Thanks for the valuable input.
Michael Lynch
Dardanelle, AR

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