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emerson

Testing if blending in crt burns really works

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I recently acquired an Amdek Video-310a MDA monitor and unfortunately it has burns in the phosphor. The burns are not as bad as some arcade monitors I've seen but still distracting when playing games. I recall the topic of fixing crt burns came up a while back so I figured I would post my results here. I realize this is not a fix and is really doing more harm than good. My IBM 5151 works well so I really don't need the Amdek and I'd rather have the knowledge then anything else. That being said, I do like the amber phosphor so if I can get it to a more tolerable state then cool.

 

Here is the monitor at the start of the test. The burns are darker in person then what's visible in the photo. What's neat are the shaded gradients on either side of the middle text for they will serve as burn-in benchmarks. I will post more pictures as the test goes on. I've never tried this before so I have no idea how long this will take.

 

1459692320_IMG_20200929_1847253651.thumb.jpg.cbe1238d8838852fa77734ecdc99273c.jpg

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It's been almost a week with no visible changes so I'm shutting it down. I figure something would have happened by now. It was worth a try.

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What does the process entail?

I'm assuming some kind of method of "burning in" the rest of the screen so it looks more even?

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14 hours ago, Asaki said:

What does the process entail?

I'm assuming some kind of method of "burning in" the rest of the screen so it looks more even?

That was the idea. I think something else is wrong with the monitor because with both internal and external brightness adjustments at max it still wasn't that bright.

 

Plus, the already burned spots might just burn more causing no visible change. I might try again when I can set up somewhere besides the middle of the floor.

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I'd create an image of the burned out spots, scale appropriately and play it back on the monitor itself.

That way, the black areas had no brightness, but the whiter areas had greater brightness... so you are effectively burning in those areas that are less burned-in, and leaving the already-burned-areas as they are.  In other words, try and display an image of the monitor's surface... on the monitor's surface.  Maybe use an image-editor to stretch the brightness so the burned out spots are black and the brightest are white... with the greys inbetween those, of course.

 

 

 

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3 hours ago, Andrew Davie said:

I'd create an image of the burned out spots, scale appropriately and play it back on the monitor itself.

That way, the black areas had no brightness, but the whiter areas had greater brightness... so you are effectively burning in those areas that are less burned-in, and leaving the already-burned-areas as they are.  In other words, try and display an image of the monitor's surface... on the monitor's surface.  Maybe use an image-editor to stretch the brightness so the burned out spots are black and the brightest are white... with the greys inbetween those, of course.

 

 

 

That is something I did not consider, good idea! The only issue is for my particular situation this is a monochrome monitor and the only pc I have that's compatible is an ibm 5150, so no image editing software that I'm aware of. I would have to create a negative image of the burned screen in text mode which is possible. 

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1 hour ago, emerson said:

That is something I did not consider, good idea! The only issue is for my particular situation this is a monochrome monitor and the only pc I have that's compatible is an ibm 5150, so no image editing software that I'm aware of. I would have to create a negative image of the burned screen in text mode which is possible. 

No, you need a positive of the burned screen. So that the black areas are still black, and the bright areas are bright!

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3 hours ago, Andrew Davie said:

No, you need a positive of the burned screen. So that the black areas are still black, and the bright areas are bright!

What I meant was a negative of the screen which burned the crt, not the crt burns themselves.

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I can see how it would work in theory, but burn-in takes so long to happen, I feel like you'd just have a monitor sitting there wasting electricity for months.

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1 hour ago, emerson said:

What I meant was a negative of the screen which burned the crt, not the crt burns themselves.

I don't think that's what you want, because the burns are a result of several screens/issues.

The screen itself gives a perfect record of what you need to "reverse" it. If indeed, it's possible.

And by "reverse" I really mean, of course, make the good bits of the screen as bad as the bad bits :P

 

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On 10/5/2020 at 10:13 AM, emerson said:

That is something I did not consider, good idea! The only issue is for my particular situation this is a monochrome monitor and the only pc I have that's compatible is an ibm 5150, so no image editing software that I'm aware of. I would have to create a negative image of the burned screen in text mode which is possible. 

Find an old Hercules graphics card and you can display graphics on the monitor, and you could probably run Windows 3.0 on the IBM 5150.

 

From experience, you could generally use a Hercules card on up to 386 PCs, some 486 and even some early Pentiums as the primary display. I set up a Pentium 66 for a friend in 1994 that used one of these monitors as the primary display until he was able to get a VGA. It would run Windows 3.1 happily. At some point the BIOSes stopped supporting these as the primary display, but even then some used a mono monitor as a secondary display alongside a VGA, and I saw this setup being used up until the late 90s, on Pentium IIs, I recall.

 

But that said, for fixing the problem, there really isn't a good way to do it. If the monitor is already not very bright, most likely the phosphors for the whole monitor are very degraded already. Even if you can crate an image to burn the good areas to the same level as the bad, the best you can hope for is for the whole monitor to be as dim as the dimmest area is currently.

 

I would liken it to getting an ugly brownish-yellow food stain on a white tuxedo that won't come out, so the best you can do is make the whole tuxedo an ugly brownish-yellow. But that is hard to do, so you dye the whole tuxedo brown so the stain is less noticeable. Neither is a great solution.

 

But, if you want to try burning the image down more, aside from maxing the brightness pot, open it up and crank up the pot on the flyback to brighten up the screen even more (not too far, though, or you may see the retrace lines on the screen), and this will accelerate the burning of the phosphors.

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Try holding a magnet just close enough to each of the larger sunspots to lighten them for a few seconds. Repeat until significantly lessened or resolved; be careful of holding the magnet for too long or too closely.

On 9/29/2020 at 7:30 PM, emerson said:

 

 

1459692320_IMG_20200929_1847253651.thumb.jpg.cbe1238d8838852fa77734ecdc99273c.jpg

 

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4 hours ago, Mr SQL said:

Try holding a magnet just close enough to each of the larger sunspots to lighten them for a few seconds. Repeat until significantly lessened or resolved; be careful of holding the magnet for too long or too closely.

What is the logic behind that exactly? Have you done this before and with what size/type of magnet do you reccomend?

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2 hours ago, emerson said:

What is the logic behind that exactly? Have you done this before and with what size/type of magnet do you reccomend?

Distortion from the magnetic field. Yes, use a greater distance to the screen based on the strength of the magnet. 

 

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5 hours ago, Mr SQL said:

Try holding a magnet just close enough to each of the larger sunspots to lighten them for a few seconds. Repeat until significantly lessened or resolved; be careful of holding the magnet for too long or too closely.

 

Magnets only affect color purity on color CRTs. this is why color CRTs have degaussing coils but monochrome CRTs do not. If you put a magnet on it you’ll likely just see a momentary distortion of the electron beam to the screen around the magnet, which will go back to normal once the magnet is removed. 

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8 hours ago, batari said:

Magnets only affect color purity on color CRTs. this is why color CRTs have degaussing coils but monochrome CRTs do not. If you put a magnet on it you’ll likely just see a momentary distortion of the electron beam to the screen around the magnet, which will go back to normal once the magnet is removed. 

This was my thought as well. I don't see how it would affect burnt phosphors.

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10 hours ago, Mr SQL said:

Distortion from the magnetic field. Yes, use a greater distance to the screen based on the strength of the magnet. 

 

The burned areas are because of the degradation of the internal phosphor coating's luminence due to the electron beam "burning" the phosphor at those locations. Using a magnet to focus even more electrons the areas affected isn't going to make them any less-burned. I don't see how a magnet can be of any use at all in this situation.

 

 

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10 hours ago, Andrew Davie said:

The burned areas are because of the degradation of the internal phosphor coating's luminence due to the electron beam "burning" the phosphor at those locations. Using a magnet to focus even more electrons the areas affected isn't going to make them any less-burned. I don't see how a magnet can be of any use at all in this situation.

 

 

 

11 hours ago, emerson said:

This was my thought as well. I don't see how it would affect burnt phosphors.

20 hours ago, batari said:

Magnets only affect color purity on color CRTs. this is why color CRTs have degaussing coils but monochrome CRTs do not. If you put a magnet on it you’ll likely just see a momentary distortion of the electron beam to the screen around the magnet, which will go back to normal once the magnet is removed. 

The phosphor coating is magnetic so it may depend how badly it's burned. If leaving the set on maximum brightness has done nothing it's worth trying. There are magnets for convergence in some sets.

 

 

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Remember those monitor calibrators for pro-level graphics apps? Take it a step further.

 

Make an inverted mask and mix it with the video signal. Like a phosphor mask in MAME, but custom to this specific tube. When the beam scans over the dark area, the image is amped-up. And when scanning over a light area, the image is darkened.

 

Feed the user's source video signal into an R-Pi and have it apply the inversion filter realtime.

 

And to go a step further. Automate it. All you'd need is 4 pictures of the crt, RGB + white. Have software analyze the burn in and create the mask for you. Or do even that in realtime by pointing a camera at the CRT and have the software analyze the burn-in straight away.

 

Possible? Absolutely. And as a bonus, you could do this every year as the tube ages. It's similar to compensating for hot pixels in a DSLR by using a dark frame.

 

Gosh I love myself for coming up with these ideas!

 

Edited by Keatah

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22 minutes ago, Keatah said:

 

Make an inverted mask and mix it with the video signal. Like a phosphor mask in MAME, but custom to this specific tube. When the beam scans over the dark area, the image is amped-up. And when scanning over a light area, the image is darkened.

 

Feed the user's source video signal into an R-Pi and have it apply the inversion filter realtime.

 

You should read other posts in this thread :)

 

According to me, you do NOT want an inverted mask of the screen, but actually a positive mask.

Where the screen is dark, you want dark. Where the screen is light, you want light. You effectively want to degrade the non-burned-in areas so that they are more like the burned-in areas. That's my theory.

 

You can't "repair" the burned-in areas; the phosphor in those areas is no longer capable of glowing with sufficient luminance, despite how many electrons you bombard it with.

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43 minutes ago, Andrew Davie said:

According to me, you do NOT want an inverted mask of the screen, but actually a positive mask.

Yes of course I knew that!

 

43 minutes ago, Andrew Davie said:

You can't "repair" the burned-in areas; the phosphor in those areas is no longer capable of glowing with sufficient luminance, despite how many electrons you bombard it with.

Then it's time to replace it. I knew that too!

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4 hours ago, Mr SQL said:

 

The phosphor coating is magnetic so it may depend how badly it's burned. If leaving the set on maximum brightness has done nothing it's worth trying. There are magnets for convergence in some sets.

 

 

The convergence magnets are for the red, green and blue cathode rays to line up properly. Monochrome monitors don't have any convergence to deal with. Plus, the magnets are on the neck of the CRT, not anywhere near the screen.

 

A degraded phosphor has actually undergone chemical changes. What is potentially "magnetic" is the aperture grille or shadow mask, a steel plate behind the screen, but again, this is only present on color CRTs to let the blue, green and red rays through their own individual slots on it, and it actually isn't supposed to be magnetized at all (thus the degaussing coils, that are to demagnetize it.)

 

 

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17 hours ago, batari said:

The convergence magnets are for the red, green and blue cathode rays to line up properly. Monochrome monitors don't have any convergence to deal with. Plus, the magnets are on the neck of the CRT, not anywhere near the screen.

 

A degraded phosphor has actually undergone chemical changes. What is potentially "magnetic" is the aperture grille or shadow mask, a steel plate behind the screen, but again, this is only present on color CRTs to let the blue, green and red rays through their own individual slots on it, and it actually isn't supposed to be magnetized at all (thus the degaussing coils, that are to demagnetize it.)

 

 

Yes the magnets are balanced for convergence and only on the color sets.

 

Agree about the degaussing coils but those are also only on color sets. 

 

I did a search and saw the same idea I suggested here on the Antique Radio Forums:

 

"you could lessen burn-in by swiping a magnet back and forth over the area, with video on the screen, in
as many directions (incidental angles)..."

 

If think perhaps what is happening is that some free phosphor sticks to the existing phosphor that remains in the burned area if the burn is not that bad as phosphor is also magnetic. 

 

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