ZX81 generates high pitched sound on CRT

Discussions about Sinclair ZX80 and ZX81 Hardware
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mrtinb
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Re: ZX81 generates high pitched sound on CRT

Post by mrtinb »

I the weekend I'll check if I can see some blue sparks in the dark.
Martin
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dessony
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Re: ZX81 generates high pitched sound on CRT

Post by dessony »

To people who don't understand German, I just web-translated Tiger's message into English:

[ Maybe you can understand German because unfortunately, I can't put it this way in English: In the case of tube devices (CRT), a line transformer is used in the high-voltage part, which generates a high voltage to the image tube. Over the years, these transformers somehow draw moisture and then the insulation of the transformer coils becomes brittle. This leads to high-voltage jumps, which often manifest themselves in the sounds you describe. The sparks that skip can sometimes be seen: it is small blue arcs that occur with these sounds. In such cases, the line transformer should be replaced immediately, because sooner or later the high voltage will collapse and your CRT will no longer provide a picture ... ]

CRT is Cathode Ray Tube [ for people who don't understand the electronic terms. ]

A line output transformer is the same as a flyback transformer. See https://en.wikipedia.org/wiki/Flyback_transformer

Cheers,
DesSony
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Tiger
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Re: ZX81 generates high pitched sound on CRT

Post by Tiger »

@ dessony - thank you
@ mrtinb
maybe you can hear the sound with the ZX81 connected is that you get a mostly white screen. So the CRT needs a higher high tension level. I think you'll also hear this pitched sound with other equipment's that produce a bright video-signal.
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mrtinb
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Re: ZX81 generates high pitched sound on CRT

Post by mrtinb »

I use Andy's ULA, and often inverse the whole screen. Then it is white text on black screen. This also generates the sound. So I don't think it's related to black text on white screen.
Martin
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1024MAK
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Re: ZX81 generates high pitched sound on CRT

Post by 1024MAK »

Does running in FAST mode make a difference?

Mark
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Re: ZX81 generates high pitched sound on CRT

Post by dessony »

mrtinb,

What are your monitor's brand name and its model number? We might find a schematic and troubleshoot a source of the noise. After opening your monitor's back case, a good chance that you will see these electrolytic capacitors' tops might be bulged or "dried" leaked from its bottoms. Cold or dry solder is possible. And, don't forget to check a horizontal output transistor's [ H.O.T. ] current status.

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DesSony
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mrtinb
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Re: ZX81 generates high pitched sound on CRT

Post by mrtinb »

Eagle CSS40 System CSS-14 Series, CCTV System. Monitor Model P701 (HVM29XXAS4C).

Can't find anything about it.

Sound is off, when LISTing i FAST-mode, but the resumes, when picture is drawn again.
Martin
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Re: ZX81 generates high pitched sound on CRT

Post by mrtinb »

I have now opened the back of the monitor.

I have taken 2 pictures of the back if the tube in operation.
  • One picture was taken with no composite input,
  • and the other when the text mode of ROM display routine is making the sound.
You can see it is shining brighter and more blue, when the text mode is there with the sound.

Image

Image
Martin
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Re: ZX81 generates high pitched sound on CRT

Post by 1024MAK »

Does the sound change at all if you vary the brightness between normal and minimum? Try the same with the contrast control?

In your photos, the yellow/white light is most likely the heater for the cathode (just like any valve / tube, the cathode must be kept hot to aid the electron flow).

From the photos, I’m not sure, is the blue light coming from inside the tube?

A photo showing the inside in daylight with the monitor in the same position would help.

Mark
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Re: ZX81 generates high pitched sound on CRT

Post by mrtinb »

The sound does not change at all changing the contrast and brightness.

And here is a picture without the lights turned off. Here the monitor is powered off as well.

Image
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
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