Testing if blending in crt burns really works

[+Andrew Davie]

24 minutes ago, Mr SQL said:

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)..."

 

 

The last two posts in that very same thread debunk the suggestion. In as many words, "ain't gonna happen".

 

[Mr SQL]

7 hours ago, Andrew Davie said:

 

The last two posts in that very same thread debunk the suggestion. In as many words, "ain't gonna happen".

 

You and batari are both old-school engineers like me so should keep an open mind; consider we only come across new ideas by experimenting, only academics and their students can avoid them using simple idioms.  

 

I am not impressed by the debunkers on the thread or the OP's engineering knowledgebase for that matter or he would not need the advice.

 

I think the idea is sound and worth a try in case the particular phosphor compound is magnetic or can be magnetized- that's what was described in the post, have you ever work a magnet over a screwdriver or paperclip like that when you were a kid? 

 

It gets magnetized and it becomes a magnet too, magnetic fields are transferrable and that's the idea there with phosphor accumulation but the trouble is there are many types of phosphor and not all are equally magnetic so I think the OP would have to experiment to see if it helps.

 

[+Andrew Davie]

Since I have read-up on, and mostly understand the mechanism of the darkening... and also since I have some formal training as a scientist...

 

The ZnS phosphors in CRTs degrade through several mechanisms, including surface excitation and build up of electric charge. Reactions on the surface of such phosphors caused by bombardment with electrons are directly correlated to the loss of brightness.  The specific mechanism of degradation is the reduction of the metal ions of the phosphor through captured electrons. The ionic phase of the phosphor is reduced to a non-ionic phase, which is what we see as a darkening of the phosphor layer.  The darkening is proportional to the exposure to electrons (i.e., the degradation extent).

 

So, you're left with a requirement for your magnet to convert the "dark" non-ionic neutral metallic phase to a positively charged (2+) ionic phase which can once again emit photons when bombarded with electrons. With magnets.

 

Yeah, nah.

 

 

[+batari]

Based on my own knowledge, I predict that this won’t work, and I’ve given a reason why: degraded phosphors undergo chemical changes. A magnet, on the other hand, does not chemically change the material it magnetized. All magnetizing does is align the spins of the electrons in a material.

 

i can’t say if the phosphor can be magnetized in this fashion or not, but regardless, I don’t think magnetization will brighten anything. It is not magnetization that causes the phosphorescence. 

 

Also the phosphor coating isn’t like the “Hairy Harry” magnetic toy we had as kids where we can move magnetic particles around at will. It is designed to stay put.
 

But by all means, try it anyway though. If only for an exhaustive scientific proof of what is being discussed here. 

[Mr SQL]

On 10/15/2020 at 3:08 AM, batari said:

Based on my own knowledge, I predict that this won’t work, and I’ve given a reason why: degraded phosphors undergo chemical changes. A magnet, on the other hand, does not chemically change the material it magnetized. All magnetizing does is align the spins of the electrons in a material.

 

i can’t say if the phosphor can be magnetized in this fashion or not, but regardless, I don’t think magnetization will brighten anything. It is not magnetization that causes the phosphorescence. 

 

Also the phosphor coating isn’t like the “Hairy Harry” magnetic toy we had as kids where we can move magnetic particles around at will. It is designed to stay put.
 

But by all means, try it anyway though. If only for an exhaustive scientific proof of what is being discussed here. 

X2 I'm not promising the OP it's going to work either just that it's a good experiment. 

 

Just like the Hairy Harry magnetic toy we had as kids there may be enough free phosphor to magnetize and accumulate on the remaining phosphor in the dark spots, worth a try.

 

On 10/15/2020 at 2:01 AM, Andrew Davie said:

The ZnS phosphors in CRTs degrade through several mechanisms, including surface excitation and build up of electric charge. Reactions on the surface of such phosphors caused by bombardment with electrons are directly correlated to the loss of brightness.  The specific mechanism of degradation is the reduction of the metal ions of the phosphor through captured electrons. The ionic phase of the phosphor is reduced to a non-ionic phase, which is what we see as a darkening of the phosphor layer.  The darkening is proportional to the exposure to electrons (i.e., the degradation extent).

 

 

Excellent detailed description of degradation - what are your thoughts on the Hairy Harry analogy to adhere free non-degraded phosphor by creating a permanent magnetic field on it for targeted binding on the degraded areas?

 

Here is an explanation of the science behind the technique that was described:

 

[+Andrew Davie]

53 minutes ago, Mr SQL said:

what are your thoughts on the Hairy Harry analogy to adhere free non-degraded phosphor by creating a permanent magnetic field on it for targeted binding on the degraded areas?

 

1) The particular phosphor would need to be strongly magnetic. There is little to suggest phosphors used in CRTs are magnetic at all.

2) There would need to be loose/free/mobile non-degraded phosphor available inside the CRT.

3) You somehow have to be able to move that phosphor to the areas where you want it to be.

4) You have some mechanism to hold/stick it in place.

 

I've replied since you asked me a direct question, but I'm not really interested in pursuing this further.

There's probably a pretty good reason there's a scarcity of literature on repairing CRT phosphors.

 

With regard to changing the ionic state via magnetism, my son, who has a degree in Chemistry, says...

 

"I haven't really heard of magnets changing oxidation state, but if so what you'd be looking for is something along the lines of "magnetic redox/oxidation of phosphorus" or whatever compound is in a CRT... but to be honest redox chemistry (what you're asking about) is generally a chemical process"

 

I will leave it at that. I don't particularly want to argue the point any more.

Good luck with any experiments!  

 

[alex_79]

15 hours ago, Andrew Davie said:

There's probably a pretty good reason there's a scarcity of literature on repairing CRT phosphors.

A guy told me that applying some holy water with a soft brush to the crt surface will help the magnet doing its stuff.
This apparently is due to the phosphor coating transubstantiating into a magnetic powder so it can be moved into the burned areas.
Of course you won't find this mentioned in scientific literature as those academics and their students are too closed-minded.?

 

[Securedcollar]

On 9/29/2020 at 4:30 PM, emerson said:

 

 

 The way to 'fix' burn in is to have an image that is all 'white' but has the burnt in part as black, matching pixel to pixel to the burnt areas, with intensity adjusted pr. pixel if possible.

 But all this is doing is causing burn in on the rest of the screen so they match the areas already with burn in.

 This results in a much darker screen. You can turn the brightness even higher to compensate for this, but then the monitor is drawing much more power, putting more strain on aging components, and you are just delaying the inevitable.

 So the only realistic options are to live with the existing burn in or just write off the display.
 

[Keatah]

A cheap way is to just paint over with amber paint. Use a magnifying glass for extra precision.

 

If have $$$ to spend, try an automotive tint shop.

[+-^CrossBow^-]

Smoked plexi is sometimes used in the arcade world to minimize the visibility of burn in on arcade CRTs. Sure it is still there, but it helps to minimize being able to see it when the screen is off and helps blend in when powered on.

 

[emerson]

Thanks to everyone for the suggestions but I gutted this monitor for the usable parts and threw the rest away over a year ago when I found another amber monitor with notably less burn.