CRT Display Fault

Jun 18, 2025 Last reply: 2 months ago 3 Replies
C

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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E

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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C

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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P

That symptom does sound like it could be related to the vertical deflection section. I’d also take a close look at any electrolytic capacitors around that area, even if they don’t show obvious signs of damage. On older CRTs, dried-out caps can cause some really strange display issues before they fail completely.

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