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Old 04-15-2018, 09:53 PM
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Electronic M Electronic M is offline
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Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
On color CRTs I've seen that at least 5 times by now...At least that is small and it does not appear to have completely ruined any single phosphor dot. I have one half the size of a pea and, one where a single color dot is dead and one where a single color dot is the wrong color (was it R gee bee or R bee gee ). The bigger the more noticeable. The other two cases are also bad as on solid colors that show primary purity they stick out like a sore thumb.

Sometimes it is a manufacturing defect, one other possibility (though I've only seen it on B&W sets) is there was no gun suppression on power off...That bright dot in the center* after each power off cycle can burn the phosphor off (color sets usually bothered to suppress it).
*Centering and other factors can move it off center a bit.

Another possibility on some tubes is leaving the tube open too long in the rebuilding cycle and allowing rust to grow in the shadowmask blocking one or more holes.
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