This CRT is a Hyundai HN-4850, sold under the brand name KTX. A while ago, I fed it a video signal at a greater frequency than it was designed to handle, and after a spell of cutting out, jerking image, odd 'crack' and 'Fzxzsxch' noises, it stopped working altogether, and only made a repeated click sound, and the amber standby light flashed. I looked up the issue, it appears to be caused by a bad Horizontal Output Transistor (HOT). I ordered a new one, but in the meantime I found another CRT, and installed its HOT into mine. It made the same noise it used to, (the "Fzsxcxsh" sound) and the same weird white flash at the edges of the screen, before going back to the repeated clicking and flashing. Clearly the HOT was only a casualty suffered as a result of another bigger issue somewhere else. Could anyone tell me what the issue might be, and how I might be able to fix it?

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    Your analysis seems to be correct, there is more damage for sure. Video signals with a greater frequency than permitted can lead to erroneous voltages in the monitor, which can destroy anything. The professional way will be to search for a service manual and schematic, and to use your oscilloscope to check systematically. This is not a beginner's task and potentially dangerous for your health and life. Aug 31, 2021 at 6:14
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    Can anybody clarify what a HOT is?
    – Tommy
    Aug 31, 2021 at 6:29
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    @Tommy Horizontal Output Transistor.
    – Justme
    Aug 31, 2021 at 6:35
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    Shouldn't this be more a question for electronics.stackexchange.com?
    – chthon
    Aug 31, 2021 at 14:38
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    odd 'crack' and 'Fzxzsxch' - the Retrocomputing-era (and possibly non-politically correct) terminology used to be "Spitzensparken und Flaschenpoppen" IIRC. "Releasing the magic smoke" just doesn't sound the same :)
    – alephzero
    Aug 31, 2021 at 14:53

1 Answer 1


I get the impression that you're not a trained monitor or TV set technician with CRT experience.

I can only recommend to stay away from the circuitry inside a CRT, as there are deadly high voltages (way higher than line voltage!) inside, even minutes after switching off.

Your life is at risk, really!

So, if the CRT is worth it, get an old-school technician to do the necessary repair. But probably you're better off looking for a replacement.

  • I think this should be a comment. It is a nice suggestion and warning but does not answer the question why the transistor keeps failing, what could be the issue or how to fix it.
    – Justme
    Aug 31, 2021 at 11:01
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    Yes, I thought about doing it as a comment, but as an answer it's more prominent. (And maybe, "get a technician" might count as an answer...) Aug 31, 2021 at 11:04
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    Maybe we could have a canonical duplicate ‘I have a broken CRT, how can I repair it if I have never done that before? / Don’t’ question-answer pair on this site? Aug 31, 2021 at 13:26
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    This was posted as an answer, but it does not attempt to answer the question. It should possibly be an edit, a comment, another question, or deleted altogether.
    – user253751
    Sep 3, 2021 at 11:41
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    @RalfKleberhoff Stack Exchange doesn't care why you wrote a comment as an answer. The fact is that the answer box is strictly only for answers.
    – user253751
    Sep 3, 2021 at 12:22

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