From Newsgroup: sci.electronics.repair

Gentlemen,

I have a spectrum analyzer with a display problem. Forget the precise
make and model for once; this is a common display issue affecting
*all* CRT displays. Let me describe what I'm seeing...
At first switch-on, there's no picture at all; just an elongated,
fuzzy blob on the screen. Over the course of the next few minutes,
this fuzzy blog gradually expands and reveals the image it should
display. However, this image, even after an hour or more, never gets
beyond about a third of the size it should be. I can make out what
it's *trying* to display; all the information is present there, but
it's compressed and fuzzy (and a bit twitchy as well).
I'm sure I've encountered this issue with CRTs many times over the
past 60 years, but I'll be f***ed if I can remember what causes it.
Any ideas?

CD.
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From Newsgroup: sci.electronics.repair

On 6/18/2025 1:11 PM, Cursitor Doom wrote:

Gentlemen,

I have a spectrum analyzer with a display problem. Forget the precise
make and model for once; this is a common display issue affecting
*all* CRT displays. Let me describe what I'm seeing...
At first switch-on, there's no picture at all; just an elongated,
fuzzy blob on the screen. Over the course of the next few minutes,
this fuzzy blog gradually expands and reveals the image it should
display. However, this image, even after an hour or more, never gets
beyond about a third of the size it should be. I can make out what
it's *trying* to display; all the information is present there, but
it's compressed and fuzzy (and a bit twitchy as well).
I'm sure I've encountered this issue with CRTs many times over the
past 60 years, but I'll be f***ed if I can remember what causes it.
Any ideas?

CD.

Could be a high voltage supply problem,
maybe a leaky HV capacitor.

Generic Troubleshooting:
Rule 1: Check the voltages.
Rule 2: See rule 1

Ed
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From Newsgroup: sci.electronics.repair

On Wed, 18 Jun 2025 16:07:05 -0400, ehsjr <ehsjr@verizon.net> wrote:

On 6/18/2025 1:11 PM, Cursitor Doom wrote:

Gentlemen,

I have a spectrum analyzer with a display problem. Forget the precise
make and model for once; this is a common display issue affecting
*all* CRT displays. Let me describe what I'm seeing...
At first switch-on, there's no picture at all; just an elongated,
fuzzy blob on the screen. Over the course of the next few minutes,
this fuzzy blog gradually expands and reveals the image it should
display. However, this image, even after an hour or more, never gets
beyond about a third of the size it should be. I can make out what
it's *trying* to display; all the information is present there, but
it's compressed and fuzzy (and a bit twitchy as well).
I'm sure I've encountered this issue with CRTs many times over the
past 60 years, but I'll be f***ed if I can remember what causes it.
Any ideas?

CD.

Could be a high voltage supply problem,
maybe a leaky HV capacitor.

Generic Troubleshooting:
Rule 1: Check the voltages.
Rule 2: See rule 1

Ed

Yes, my thoughts exactly. I'm very much hampered by a lack of decent schematics, however. In particular, expected voltage levels at the
various test points. With up to 3kV present in this area, I'm not
prepared to take chances. At this point in time, I shall most likely
bin the CRT and go for one of those LCD conversion kits. Expensive,
but worth it.
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