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Old 20th Mar 2017, 3:19 pm   #1
AnalogueMatty
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Default Removing light scratches from CRT screen - possible ?

My latest acquisition, a Ferguson Colourstar, has a couple of light vertical scratches on the screen, as if dust has been swept off with a ringed finger . Only noticeable on some of the brighter pictures - does anyone have any tips on polishing these out ?
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Old 20th Mar 2017, 3:27 pm   #2
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Default Re: Removing light scratches from CRT screen - possible ?

You could try Wet n Dry paper around grade 400 soaked in washing up liquid but it takes a while. if it leaves fine scratches finish off with a higher grade of paper and then polish with some T Cut.

I think the official way is with jeweler's rouge if you can find it.

If you do find the rouge keep an eye on what you are doing as you could get carried away and leave a dent in the screen.
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Old 20th Mar 2017, 5:14 pm   #3
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Default Re: Removing light scratches from CRT screen - possible ?

I am not known for being H&S mad but wear goggles, the small scratches can start a full blow up.
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Old 20th Mar 2017, 5:35 pm   #4
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Default Re: Removing light scratches from CRT screen - possible ?

That reminds me of some instructions in the technical notes/manual for an early-ish workstation (the Whitechapel MG1 in case anyone remembers it). The section on adjusting/repairing the monitor included some information on protective equipment :

A face sheild to BS... to protect the eyes

Leather gloves to BS... to protect the hands

A heavy leather apron 'to protect those other precious parts'.

And that was just for tweaking the internal presets... Needless to say I did not bother when repairing mine
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Old 20th Mar 2017, 6:07 pm   #5
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Default Re: Removing light scratches from CRT screen - possible ?

I would try a metal polish such as Brasso in the first instance.
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Old 20th Mar 2017, 6:34 pm   #6
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Default Re: Removing light scratches from CRT screen - possible ?

The CRT glass is VERY hard and incredibly difficult to polish. I would leave it well alone. Scrub any dirt out of the fine scratches with a nail brush and a dilute household cleaner.
Even 1800 grade wet and dry is liable to damage the surface. Just my thoughts. John.
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Old 20th Mar 2017, 11:48 pm   #7
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Default Re: Removing light scratches from CRT screen - possible ?

Hi there,
In a previous life, as part of my TV & video repair work, I used to sell ex- rental tv's from time to time. Mainly thorn 9000's, TX9 & 10, Gll's etc. I frequently had sets with scratches on the screen and if the scratch was vertical, it would interfere with the stripe of the phosphor and be very noticeable.
At the time, I bought a tube polishing kit from a company in Ware or Hoddesdon I think. I believe it was advertised in TV magazine.
It consisted of a foam cylinder about 4" diameter attached to a shaft which you mounted in an electric drill. There was a couple of different grades of sanding belt which went round the foam. The bulk of the scratch was removed with a fairly course belt and then finished off with a fine one. You were aiming for a fine matt finish over the surface of the tube where the scratch used to be.
Once this had been achieved, it was finally polished up with what I always assumed was jeweller's rouge. This was done wet using a different foam pad.
I achieved excellent results using this kit and got pretty good at doing it. I managed to get rid of some quite major damage- certainly no one ever seemed to notice!
I worked on the assumption that the tube face is pretty thick so would not be unduly weakened and I never had any problems. Whether this was a good assumption, however, I'm not sure. I did wear a breathing mask for the sanding down.
If I needed to do so, I would use a similar technique again, but would like to experiment on a scrap tube first to regain some experience.
Certainly, if I was doing this on a pre- implosion protected tube, (ie. one with a safety glass) I would wear face and body protection just in case I have never tried on such a tube though.
Cheers Nick
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Old 21st Mar 2017, 6:42 am   #8
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Default Re: Removing light scratches from CRT screen - possible ?

Quote:
Originally Posted by 1100 man View Post
If I was doing this on a pre- implosion protected tube, (ie. one with a safety glass) I would wear face and body protection just in case I have never tried on such a tube though.
Cheers Nick
Very wise but you should never have to do this as the screen has been protected, the scratch should always be on the glass or acrylic implosion guard.

Cheers
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Old 21st Mar 2017, 6:53 am   #9
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Default Re: Removing light scratches from CRT screen - possible ?

I am with the leave it alone brigade , I have seen it done professionally the whole screen has to be done, Mick.
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Old 21st Mar 2017, 6:59 am   #10
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Default Re: Removing light scratches from CRT screen - possible ?

Although the glass is thick, I agree that a significant scratch might act as a stress-raiser, and could possibly lead to an implosion.
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Old 21st Mar 2017, 7:57 am   #11
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Default Re: Removing light scratches from CRT screen - possible ?

Cerium oxide on moist chamois leather is the recommended way to polish scratches out of a car windscreen, so it may work on a CRT face.

Various kits are available from eBay suppliers. Some contain various different grades of cerium oxide powder.

Martin
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Old 21st Mar 2017, 10:15 am   #12
AnalogueMatty
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Default Re: Removing light scratches from CRT screen - possible ?

Thanks for the replies, I will carefully consider these options - I wouldn't want to risk making matters worse. I'm more focused on monitoring the set's reliability before I tackle aesthetic improvements. Best regards folks !
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Old 21st Mar 2017, 10:19 am   #13
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Default Re: Removing light scratches from CRT screen - possible ?

I have only ever used Brasso or Farc something that is used on car paintwork.
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Old 21st Mar 2017, 11:11 am   #14
John M0GLN
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Default Re: Removing light scratches from CRT screen - possible ?

I once had a scratch polished out of a car windscreen, from outside of the car it looked perfect but from inside objects seen through the polished area were quite distorted and I had to replace the screen, this may be because of the distance of the objects from the windscreen, perhaps with a TV screen where the distance from image to outer glass surface is quite small there would be no noticeable distortion.

John
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Old 21st Mar 2017, 12:16 pm   #15
dseymo1
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Default Re: Removing light scratches from CRT screen - possible ?

I wonder if you could fill the scratch with UV-curing glass adhesive?
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Old 21st Mar 2017, 1:53 pm   #16
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Default Re: Removing light scratches from CRT screen - possible ?

Isn't there such a product for disguising cracks in car windscreens? Might not work on fine scratches though.

e.g. http://www.ebay.co.uk/itm/like/13172...8466455&crdt=0
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Old 21st Mar 2017, 10:34 pm   #17
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Default Re: Removing light scratches from CRT screen - possible ?

Solvol Autosol is basically jewellers rouge in a gel carrier - I've cut loads of optical quality plastics etc. with it [e.g. oxidised car headlamps and IR remote lenses etc.] - can't say I've ever needed to use it on glass tho' .... but would give it a go if I had to.

However .... I do note all the counsel and caution re. CRT's.
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Old 22nd Mar 2017, 8:38 am   #18
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Default Re: Removing light scratches from CRT screen - possible ?

I remember back in my TV days when the tube gunning technician had a returned tube with a deep scratch. He used jeweler's rouge and managed to get it out well. The screen was as smooth as anything but there was a noticeable 'dent'
I would have been concerned about the strength of the tube with this deep depression but it was obvioulsy useless for vision! Personally I would have no fear of polishing out light scratches.

Seriously though - I have used Solvol Autosol and similar for scratches on car screens. I once had a really frightening experience with a plank blowing off a lorry and hitting my windscreen flat! It left a dent which took some polishing out!
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Old 22nd Mar 2017, 12:40 pm   #19
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Default Re: Removing light scratches from CRT screen - possible ?

Quote:
Originally Posted by ionburn View Post
I once had a really frightening experience with a plank blowing off a lorry and hitting my windscreen flat! It left a dent which took some polishing out!
I don't quite understand how an impact can dent glass without breakage

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Old 22nd Mar 2017, 12:44 pm   #20
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Default Re: Removing light scratches from CRT screen - possible ?

I had the same kit as Nick mentions in post 7. It was useful up to a point, but I usually only used the 'rouge' to poish the screens. Really bad scratches were asking the impossible. You could get rid of them, but it did leave a flat area. Also odd parallax effects could be seen.
When selling an ex-rental, I'd show it working, then tell the customer there was a scratch on the screen and I'd knock a tenner off. I'd then challenge them to spot it. Usually they couldn't find it till it was switched off. And if they could then there was always another TV for sale!
Glyn
PS The main problem with using this kit was the faceplate could become worryingly warm when using the drum sander on a drill, so you needed to be careful.
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