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CRT monitor color issue

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kaneda23

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Feb 9, 2024
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I have a Magnavox CM9043 EGA monitor that is showing some color distortion at the top and bottom of the screen. I created a BASIC program to change the background color between red, green, and blue to show the issue. Here is my attempt to capture the monitor showing each of these colors.

red:
ega-monitor-red.jpeg
I didn't get a good picture of it, but it is showing blue-purple at the top, and green at the bottom

green:
ega-monitor-green.jpeg

blue:
ega-monitor-blue.jpeg

I'm assuming that this a monitor issue, but I don't have another CGA/EGA card to test with it. Is it an issue with the screen becoming magnetized?

Thanks!
 
It could be magnetized, but the built in degaussing coil should take care of that unless it's malfunctioning. If someone was playing with a large magnet, then it is possible to magnetize it too strongly for the built in degaussing coil to fix it. If it was dropped, the shadow mask may have shifted out of position.

Assuming you don't own a degaussing coil, you can use a bulk tape eraser. Just turn it on a few feet from the screen, gradully move it closer, then wave it around the screen, and gradually move away before turning it off.
 
THese are readily available and good value.

www.ebay.com.au

Mini Degaussing Wand Portable Coil Demagnetizer Degausser Arcade | eBay

You will get : You will receive 1pcs Degausser Degaussing Wand Coil Demagnetizer. For Degaussing issue only,other issues than what this tool Could fix.
www.ebay.com.au

Only ever do it from the front of the CRT , moving the wand in a circular motion and prgressively moving it away from the faceplate. Never apply the wand to the tube bulb or neck area inside the set, and never near any populated pcb's or anything that has any magnetic storage media, The high field can be very destructive. Also don't hold the button down for more than about 5 seconds as these wands heat up fast.

There are many cases where the magnetization is not resolved by the internal degaussing coil and it needs the wand, but there is always the chance the shadow mask is warped as Andy says, you won't know untill you attempt degaussing it with the wand.
 
Thanks. I don't own a bulk tape eraser or a degaussing coil, so the linked degaussing wand seems like the least expensive option. I'm in the US, but I found a similar looking wand on Amazon:


Would this be safe to use on 110v?
 
Well, it has a standard 110VAC two-prong plug but ... I'd pay attention to the single review:

"Dangerous. Rapidly over-heated, burnt my hand.
USA plug attached, no instructions. Complete rubbish.
Refunded."
 
pbirkel@gmail.com said:
Well, it has a standard 110VAC two-prong plug but ... I'd pay attention to the single review:

"Dangerous. Rapidly over-heated, burnt my hand.
USA plug attached, no instructions. Complete rubbish.
Refunded."
Click to expand...
Well, as I mentioned in my post, you are only supposed to hold the button down for less than a few seconds, obviously the person who made that remark about the burnt hand was a total idiot. As Mr Einstein pointed out, the Universe may well not be infinite, but Human stupidity is.
 
pbirkel@gmail.com said:
Indeed. But the lack of any other reviews (pro or con) does leave one with a big caveat emptor, IMO.
Click to expand...
To make a wand that had the required peak magnetic flux and could support continuous duty would requre that it had low restance wire (preferably Silver or Gold ) wound on a ceramic former that could handle the high temperature, and it would cost 100 to 1000 times the price.

The designers assumed that the user would have "half a brain" and realised it was only for brief duty, this way they could get the price to a reasonable level to do the job required.

It is interesting how people foul up the concept of both methods or materials. In both cases there are huge potholes if people don't know what they are doing.

On one of my published projects, they tried to substitute Nichrome wire in for the Constantan (Isotan wire) wire I used. But they were clueless that in the case of Isotan you can solder to it easily, but Nichrome you cannot and that has to be crimped. Then in their bewilderment they wondered why their project failed and informed me that the design didn't work.

The odd thing is that even when specific instructions are published about how to do this or that, mostly people ignore them and think they "know better". Mostly when they do, they fall on their faces and make some outrageous remark about something "not working". I have seen it all before, very tiresome.

If there is a caveat emptor, it resides in the mind of the user who doesn't understand the Physics of the Wand.
 
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I have one of those wands that I use with a 240-110v transformer. It seems to be OK and I've never noticed it getting warm. I use it to degauss disks from time to time. It's not very strong, but should be OK for a monitor.

Here's a video of someone using one.

 
I purchased one of the mini degaussing wands and gave it a try. Happily, it seems to have mostly resolved the issue. I'm glad that the shadow mask does not appear to be damaged. Thank you to all who replied.
 
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