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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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13th Apr 2007, 3:09 pm | #1 |
Octode
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,407
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Missing phosphor dots
Hi all,
My Philips K70 has several missing phosphor dots on the screen. When the set is off they don't look any different from the rest but, when the set is on the missing phosphors are just black dots. How does this happen? Is it something that has always been since the tube was made or is it something that happens to colour tubes when old? Thanks Lee
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Lee |
13th Apr 2007, 3:23 pm | #2 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,859
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Re: Missing phosphor dots
Missing phosphor dots, or blocked holes in the shadowmask, I wonder?
Surely if the phosphor itself were missing from the faceplate of the tube, it would look different when it's off, as well as when it's on. Might be worth turning the tube faceplate-up, giving it a gentle bash, then trying again Nick. |
13th Apr 2007, 4:05 pm | #3 |
Octode
Join Date: Aug 2006
Location: Willington, County Durham, UK.
Posts: 1,499
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Re: Missing phosphor dots
Missing phosphor dots may be a sign of a regunned CRT fitted. Quite a few CRT rebuilders often used to sell them off as seconds.
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Malc Scott Last edited by Mike Phelan; 1st Jun 2007 at 7:47 pm. Reason: Typos |
14th Apr 2007, 9:45 am | #4 |
Rest in Peace
Join Date: Jun 2004
Location: Burghfield, Reading, Berkshire, UK,
Posts: 1,055
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Re: Missing phosphor dots
Hi all
In my days at the BBC, a colleague of mine was responsible for the appraisal of colour monitors coming into the BBC - it was at the time when quality, not quantity, was the most improtant thing. He often had to rejected Grade 1 monitors because of missing phosphor dots in the tubes. These tubes were relegated to Grade 2 monitors and "complete" tubes installed into the Grade 1s. This was not uncommon and vey often, the holes in the phosphor dots could be seen when the monitor was off. As the dots were deposited using the actual mask, it could be that there were blocked holes in the mask which caused the dots to be missing - chicken and egg? Cheers Brian |
17th Apr 2007, 10:15 pm | #5 |
Hexode
Join Date: Dec 2006
Location: Norwich, Norfolk, UK.
Posts: 440
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Re: Missing phosphor dots
Hi Guys
When i used to work for a large Japanese TV manufacturer, we used to get brand new tubes with flecks in the shadow mask. The girls on inspection were so good they could spot a fleck as small as 0.3mm on a red purity screen in seconds. Aparently they are caused by the final anode voltage attracting any c**p that may be in the neck at first switch on. We were sometimes sucsessfull at knocking the blockage out of the mask by banging the faceplate quite hard (hard enough to make an onlooker think it was going to go bang) with the handle of a screwdriver. Sometimes it worked, if we were lucky. Unfortunately though even if you did clear it, as soon as you switch the set off then on again, the offending piece of c**p would usually get attracted to the shadowmask again. Mike Burton |