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CGA Monitor: image shakes

N

nestor

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Jul 23, 2010
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509
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I have a Intra 14HP33T monochrome CGA monitor (white phosphor rebranded as Inves ) that has some problems. At power up, the image shows clear and crisp. Some minutes later, it starts to appear some kind of light noise or interference in the lighted zones, and minutes after the entire image starts to shake vertically (not dramatically, about only one or two lines).

What can be the cause? There are no CRT or other interference sources around. I have tested the monitor in two different computers and two different cards.
 
Temperature sensitive. You may be able to identify the faulty component by using freeze spray designed for electronics (not electrically conductive, and not corrosive).
 
If you can't find freeze spray, use a can of air duster turned up side down. Short squirts only, and be sure it's the non-flammable stuff, as things may be hot.
 
Well, It seems that now temperature is not a problem, as the monitor starts shaking when just powered on...
 
Is it mechanically sensitive, i.e. tapping side of monitor provokes/worsens jumping display?
If so, there may be a bad solder joint somewhere.
Otherwise, you may be able to identify a mechanically sensitive component by using something suitable to tap various components.
 
A wild guess, do you hear any faint popping from inside the unit sync'd with the shaking? I remember a couple monitors with a "popping" hi-voltage arc internally, and every time it arc'd the screen rolled.
 
There is no popping sync'd with the shaking, and I think it is not mechanically sensitive (tried to clap the cover and nothing changed).
 
It is worth opening up the monitor (taking the required precautions) and doing a very good visual inspection. Look at solder joints, and look at the components.
 
You describe two symptoms. When multiple symptoms present, often the best thing to do is pick one symptom, determine the symptom cause, then rectify. Quite often, in electronics, that rectification action removes other symptoms as well.

If the only symptom was the vertically jumping display, then I would have suggested to you that you think about taking a chance - replace the vertical deflection chip (if your monitor has one). Why? Because the majority (i.e. but not all) of the vertical problems (e.g. vertical collapse, vertical instability) that I have rectified over the years have been due to a defective vertical deflection chip. That is, in monitors that use a chip in the vertical section.

However, I can't see how a faulty vertical deflection chip could also cause the second symptom of "it starts to appear some kind of light noise or interference in the lighted zones".
 
Well, the noise issue is very light so maybe it is only an ageing problem. The shaking is now more perceptible and it occurs from the beginning. I recorded a video, but it is not very noticeable... I think the shake is too fast for the camera.

 
Not knowing any more that what you have shown in your video, if it it was my problem, I'd be looking at the filter caps in the monitor's power supply. That shimmy sure looks like a leaky cap to me.
 
I looked at the video a few times. I did not see a 'jumping' raster - I saw a shrinking raster. Vertically, it's varying in size (rather than staying the same size and moving up and down).

Use of freeze spray is still a worthwhile exercise. When you reach the faulty component, the instability may worsen or may lessen.

Did you do an internal visual inspection? For example, a bad solder joint is still a possibility.
 
This isn't a technical post, as I know very little about monitors, but what I can say is that my IBM 5151 (monochrome) display did that same movement although slightly more drastic - day later and it wouldn't display anything. The fix was a faulty transistor in the power circuit - replacing this repaired both symptoms.

This could be totally irrelevant to your fix, just wanted to share that in case it helps with diagnostics.
 
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