Can screen burn-in be repaired?

[barythrin]

So, this is an ignorant question but I've never quite understood what burn-in really is. This is actually stemming from my confusion yesterday on my work LCD (not at all vintage.. about 3.5yrs old) had horrible screen burn-in for the first time. I guess my screen saver didn't kick in, nor did my power management and it left my background picture on the screen all weekend so I came in yesterday to an almost cool transparent setting like a linux system but it was burn in. I turned off the monitor and back on just for kicks to see but nope it's there and I figured .. eh.. annoying but that's life and at least it's a Tux and the BSD Beastie.

It reminded me how I first heard someone say "SVGA monitors can't get screen burn-in so screen savers are now just for fun not a requirement! sweet!" and that as always proved ot to be true. However I've never had it go away like this (kinda odd, and I'm still trying to figure out if I'm just not seeing it or what.

Anyway, keeping it vintage, what *IS* the burn-in actually on? Is it the screening that ends up doing this? On this new one the burn-in was even in color lol but like a system I recently picked up (knowing it was probably going to be for parts) I could see the burn-in on the screen with the system off and unplugged on the shelf. Is this something that can be replaced or repaired inside of the CRT?

 

[RetroHacker_]

Screen burn on a CRT monitor cannot be repaired.

First, remember how a CRT works. Electrons are emitted by the gun(s) at the back/neck of the picture tube. The faceplate of the tube is coated on the back with a phosphor coating. When the electrons strike the phosphor coating, it excites the material and causes it to glow. This glow persists for a short time afterwards - and this is how the electron beam is able to scan all over the face of the tube and give the appearance of a static image.

Over time, this phosphor coating can wear out. If you display the same image in the same place for long enough, the phosphors can become "burned" or darkened from constantly being excited. In a CRT monitor, this burn-in is permanent damage to the phosphor coating. It cannot be repaired or reduced, short of replacing the entire picture tube.

The statement that SVGA monitors cannot burn in is incorrect. They can. It's just that the newer types of color tubes have better phosphors and don't tend to burn in as easily. That said, it still happens. Leave the same image on the screen too long, and it'll burn in. Burn-in happens more readily on older monochrome tubes for a couple of reasons. For one, the phosphors tend to be longer persistance, and for two, the output of machines that use monochrome screens tends to be very consistent. The first prompt is always in the same place. I've got some well-used terminals with rows of fuzzy boxes burned into the screen. The characters are always in the same place, so over time, after being abused for many years, you can make out where the character cells are.

-Ian

 

[Fallo]

Anyway, keeping it vintage, what *IS* the burn-in actually on? Is it the screening that ends up doing this? On this new one the burn-in was even in color lol but like a system I recently picked up (knowing it was probably going to be for parts) I could see the burn-in on the screen with the system off and unplugged on the shelf. Is this something that can be replaced or repaired inside of the CRT?

Basically, screen burn-in occurs when you leave a monitor running with a static picture for long periods of time, causing the phosphor to degrade and leave a ghost image. It happens more frequently in office environments where equipment is left running all the time. Monochrome monitors with long-persistence phosphor are particularly vulnerable to burn-in.

Supposedly, burn-in can be fixed by filling the screen with a bright color and leaving it like that for several hours. If that doesn't work, the only solution is to replace the picture tube.

Plasma displays are also quite prone to burn-in. Like CRTs, plasma burn-in is caused by degraded phosphor. On LCDs, burn-in is caused by pixels being stuck in the on position.

 

[RetroHacker_]

Supposedly, burn-in can be fixed by filling the screen with a bright color and leaving it like that for several hours.

That won't fix it, only mask it. It's like spilling bleach on your clothes. You can't remove the mark it made, but you can wash your clothes with bleach so that at least they're a uniform color again.

-Ian

 

[barythrin]

That's why I was a bit confused. I've only seen the inside of a tube one before but I recall some black sheet being peeled away from behind the screen, kinda leaving it see through. I was curious if that could be replaced but I guess it's more inside the glass or just unfeasible and there's nothing to replace the phosphorus coating (again.. just from what I saw that's how I expected it to be but probably incorrect).

I always did accept that burn-in was permanent but had never really though about it until these recent two events.

 

[RetroHacker_]

The "black sheet" you saw was probably the shadow mask. Color CRT's have three electron guns. to ensure that they hit the proper locations on the phosphor tube face, there is a shadow mask - screen-like piece of metal to help prevent the electrons from hitting between phosphor stripes. Monochrome CRT's do not have such a device.

Most tubes use a sheet with round holes in it. Sony Trinitron tubes, on the other hand, use a shadow mask made from fine wire - hence those one or two horizontal lines visible on Triniton tubes. These thicker wires are required to help a wire shadow mask keep it's shape. Bonk a Trinitron monitor hard on the side, and you can see the picture shimmer as the wire mask moves a bit. This shadow mask is also why color sets need to be degaussed - it can build up a magnetic field, and thus redirect the electrons as they pass, screwing up the colors. Similarly, a strong magnet can bend the shadow mask out of whack. Again, monochrome CRT's have no shadow mask, and contain nothing in the face that can be magnetized, or damaged by a magnet.

-Ian

 

[RetroHacker_]

Also, to address your questions about replacing parts inside the tube... CRT's are vacuum tubes. They are sealed, and contain a vacuum (and thus don't contain any air). If ever there was a device with no user serviceable parts, a picture tube is a prime example. Break one open at the neck, and you'll hear a loud hiss as the air rushes in, and the force of the inrush of air usually blasts some of the phosphor coating off the inside of the tube. Once the vacuum gets let out, there is no saving the tube.

The exception, of course, would be companies that used to (still?) rebuild picture tubes. To do this, the tube is placed in a controlled environment and the air slowly let in over a long period of time. Then, the neck is cut off the tube, and a new electron gun assembly is welded on. The tube is re-evacuated, pumped down, baked, and resealed. For color tubes, the electron gun assembly is the only replaceable part - the tube cannot be re-coated with new phosphor, and a damaged shadow mask cannot be replaced. For monochrome tubes, since the face is much simpler, the old phosphor coating could be cleaned out, and a new one redeposited.

The important thing to remember is that the phosphor coating on the face of the tube is only one of the things in a tube that can wear out. The cathodes in the electron guns will gradually lose emission, to the point where they don't produce enough electrons to adequately excite the phospors on the screen, and the tube gets dim. Rebuilt picture tubes were common in the 60's and 70's as affordable ways to repair television sets with worn-out tubes. Because of the ever-changing nature of television programming, the tube is very likely to lose emissions before the phosphor coating can become worn.

-Ian

 

[Fallo]

The "black sheet" you saw was probably the shadow mask. Color CRT's have three electron guns. to ensure that they hit the proper locations on the phosphor tube face, there is a shadow mask - screen-like piece of metal to help prevent the electrons from hitting between phosphor stripes. Monochrome CRT's do not have such a device.

Yes, which is why monochrome screens look perfectly smooth and not grainy. Older color TV tubes look gray because of the color of the shadow mask. At some point (it seems that the switch was made in the '90s), they started using black shadow masks on TVs.

Most tubes use a sheet with round holes in it. Sony Trinitron tubes, on the other hand, use a shadow mask made from fine wire - hence those one or two horizontal lines visible on Triniton tubes. These thicker wires are required to help a wire shadow mask keep it's shape. Bonk a Trinitron monitor hard on the side, and you can see the picture shimmer as the wire mask moves a bit. This shadow mask is also why color sets need to be degaussed - it can build up a magnetic field, and thus redirect the electrons as they pass, screwing up the colors. Similarly, a strong magnet can bend the shadow mask out of whack.

One of my TVs is an old 13" portable set from 1978. It has a greenish patch on the left side, so it appears to need degaussing. Newer sets have less metal in them, so they're not as prone to becoming magnetized, and they often have degaussing coils inside.

External degaussing coils are something that every TV repair shop used to have, but it's a old-time thing and you'd probably have to look on Ebay or your local flea market to find one.

 

[RetroHacker_]

Older color TV tubes look gray because of the color of the shadow mask. At some point (it seems that the switch was made in the '90s), they started using black shadow masks on TVs.

I don't believe you'll be able to see the shadow mask on the face of the tube with the set off. It's positioned behind the phosphor. A color tube appears gray because of the natural "deactivated" state of the phosphors, and looks grainy because of the differing colors of the phosphor stripes/triads. In the 90's, they started outlining the groups of colors with black so as to improve contrast. But the shadow mask (or the color thereof) shouldn't make a difference in the contrast.

Actually, there was a change in tube technology - from delta gun to inline gun. In a delta gun tube, the guns are arranged in a triangle at the back of the tube, and the phosphors are arranged in triads groups on the face of the tube. On an inline gun set, the electron guns are in a horizontal line, and the phosphors are deposited on the face of the tube in vertical stripes. The inline guns are much easier to converge, and simplified the electronics greatly.

Newer sets have less metal in them, so they're not as prone to becoming magnetized, and they often have degaussing coils inside.

Believe it or not, all color sets have degaussing coils built into them - even very old ones. They aren't very powerful, and fire only at powerup from being cold. TV's and older monitors don't have a user control for degauss, but it's there. They are necessary to degauss the shadow mask of the tube, as the process is rather sensitive. The Earth's magnetic field is strong enough to screw up the purity on a color tube.

Try this - if you have a CRT computer monitor, turn it sideways while it's on and displaying a picture. Look! The colors just got all screwed up. Now, press the degauss button. The colors are fixed with a POING! from the degaussing circuit. Put the monitor right side up again, and the colors return to being messed up - ready to annoy the heck out of your co-worker when he gets back to his desk (and it's even funnier if he doesn't know about the degauss function...).

-Ian

 

[barythrin]

Thanks for all the explanations. It makes much better sense to the lesser descriptions I've known about the parts. All coming together now.

Regarding degaussing the monitor, what I've done with a Sun monitor is just take almost any magnet (this wasn't an overly strong one) but I was able to "push" the bad image away. Kinda like a little degassing wand but it should still work either way if you have a CRT that doesn't have the degauss button.

 

[RetroHacker_]

Regarding degaussing the monitor, what I've done with a Sun monitor is just take almost any magnet (this wasn't an overly strong one) but I was able to "push" the bad image away. Kinda like a little degassing wand but it should still work either way if you have a CRT that doesn't have the degauss button.

You need to be careful doing this. A degaussing coil is NOT like a permanent magnet. The magnetic field alternates rapidly, as opposed to a permanent magnet, which is fixed. You run the risk of magnetizing the shadow mask even more with a permanent magnet, or with too big of a magnet, bending it.

If you need a hand-held degaussing coil, and don't have one, you can use a bulk tape eraser, or hold the handle end of a large soldering gun or power drill near the tube. These devices all emit a rapidly changing magnetic field.

You can also build a simple degaussing coil by coiling up a scavenged coil from a junk TV set, and putting a switch and a line cord on it. Be careful though - this sort of homemade coil works great, but don't leave it on for more than a few seconds, or else it can melt.

When using any kind of degaussing coil, start away from the screen, move smoothly in and back, moving the coil in circles as you do, and don't turn off the coil until you are a fair distance away.

-Ian

 

[rmay635703]

Screen burn on a CRT monitor cannot be repaired.

It can be but the time and effort required is stupid long.

Years ago the dentist office had terminals that had a negative/positive button.

If an image burned in you simply would show the same image on the negative mode so all the bright places were dark and all the dark were light and eventually the screen was not burned in as badly

Something similar can be done to color CRTs if you scan the screen in each of its 3 colors at full intensity, turn up the CRT voltage in the back and send back the "scanned" version of the screen back into the screen. By increasing the voltage and brightness you can burn in the screen more evenly, you have to check every once and a while until the burn in is less noticable. I say "more" because the screen will still not be 100% perfect but I've seen them end up pretty darn good. I actually bought a 21" screen that had this done many many years ago, there was some small fuzzyness but you couldn't really tell what the burn in was and the screen was more or less even except in the far corner.

The trouble here is it can take months to fix burn in and even once you do the screen isn't perfectly even. Back when monitors were worth a lot more than they are now some "used" pc places used these methods to get more money for otherwise useless screens.

I have no idea if these methods work on an lcd however.

 

[Chuck(G)]

What I've never been able to find out is what the mechanism is in phosphor burn. Clearly, the chemical composition doesn't change, so what happens to a phosphor, say, zinc sulfide, to make it less responsive?

White LEDs, fluorescent lamps, CRTs, plasma displays, EL displays, etc. all exhibit phosphor degradation.

Putting a screensaver on your LCD display is definitely counter-productive, as they are backlit when a display is present and the phosphors in the backlight will degrade.

 

[Agent Orange]

Burn-in is a result of the "aquadag" coating being disapated (burned away) by a concetrated stream of electrons focusing in a specific area.

Agent Orange

 

[Ec1564]

If you have a LCD monitor with "burn-in" just make sure you have some video that is not the same as what's "burnt in" in a few days hopefully the LCD pixels will recover. I get this every so often in my line of work in comsumer electronics(TV's). So far I have not ever replaced a LCD panel for image burn in like I used to with phospher based TV's!

Now on CRT projo TV's I was replacing the green and blue CRT's after customers burn't in the stock market channel or video game scores. What happens is the phosphor does a chemical change due to heat from the electron beam striking it heating it up past a point where it changes. There is no fix for it besides opening up the tube and replacing the phosphor coating which is $$$$$$$$$$$$$$$$$$ to do(CRT rebuilding) I don't think that company is around now too....

 

[Ole Juul]

The big studio monitors we had when I worked in TV had a button right on the front for degaussing. They were pretty high quality items.

Regarding the actual mechanism for phosphor burn I would have guessed something like what Agent Orange just said. I wonder though, is there not metal atoms being deposited from the cathode? You see metal being evaporated in light bulbs and vacuum tubes, of course, get nice deposits on one side.

 

[Chuck(G)]

Burn-in is a result of the "aquadag" coating being disapated (burned away) by a concetrated stream of electrons focusing in a specific area.

Most modern tubes have 'dag only on he outside of the funnel. The interior has had a coating of aluminum on most tubes since the 60's. At any rate, as the aquadag even on an older tube is present in the funnel and not the screen, the beam isn't focused there.

And vaporization of the 'dag doesn't explain why white LEDs and fluorescent lamps lose their luminosity. Or why those "forever light" EL nightlights go dim.

 

[Fallo]

A color tube appears gray because of the natural "deactivated" state of the phosphors

Same with monochrome tubes.

and looks grainy because of the differing colors of the phosphor stripes/triads. In the 90's, they started outlining the groups of colors with black so as to improve contrast. But the shadow mask (or the color thereof) shouldn't make a difference in the contrast.

My old 13" TV does have rather pale-looking colors compared to my other two sets (both from the '90s).

Believe it or not, all color sets have degaussing coils built into them - even very old ones. They aren't very powerful, and fire only at powerup from being cold. TV's and older monitors don't have a user control for degauss, but it's there. They are necessary to degauss the shadow mask of the tube, as the process is rather sensitive. The Earth's magnetic field is strong enough to screw up the purity on a color tube.

In fact, I've noticed that all my TVs and monitors make a clicking sound when powered on, which must be the degaussing coil. Incidentally the only one that doesn't is my 5151, which being a monochrome monitor, has no coil.

Try this - if you have a CRT computer monitor, turn it sideways while it's on and displaying a picture. Look! The colors just got all screwed up. Now, press the degauss button. The colors are fixed with a POING! from the degaussing circuit. Put the monitor right side up again, and the colors return to being messed up - ready to annoy the heck out of your co-worker when he gets back to his desk (and it's even funnier if he doesn't know about the degauss function...).

In fact, I'm typing this on just such a monitor. The picture turns a shade of purple when you tilt it to one side, but then returns to normal as soon as you set it back upright (without even pressing the degauss button).

 

[Druid6900]

If the degaussing circuit in a monitor fails, you can turn it on, put a monitor with a working degaussing coil up to it so that the CRTs are touching and turn on the second one.

At that distance, the field should be strong enough to degauss both of them.

 

[shawn510]

If the degaussing circuit in a monitor fails, you can turn it on, put a monitor with a working degaussing coil up to it so that the CRTs are touching and turn on the second one.

At that distance, the field should be strong enough to degauss both of them.

I've seen this effect in computer labs where CRTs are side by side. Turn one on and watch the effect move like a wave.