NotTaR of Television Sets : Comments on color purity, set orientatio..  
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Comments on color purity, set orientation, and doming

"The problem with my TV is that bright parts of the picture change color. For example, white areas may shift towards yellow or blue depending on the orientation of the set.

What are the possible causes of doming? I have noticed that the magnitude of the doming effect varies with TV orientation even after degaussing several times at the new orientation. Does this help identify the cause of the doming in my case?"

(Portions from: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)

The problem with regular shadow masks is 'doming'. Due to the inherent principle of shadow masks, 2/3 or more of all beam energy is dissipated in the mask. Where static bright objects are displayed, it heats up several hundred degrees. This causes thermal expansion, with local warping of the mask. The holes in the mask move to a different place and the projections of the electron beams will land on the wrong colours: purity errors. The use of invar allows about 3 times more beam current for the same purity errors.

Both local doming and magnetic fields compete for the remaining landing reserve. Due to improper degaussing, the doming problem may be more visible. And applying a tube designed for the wrong hemisphere may very well increase the doming complaints. It is possible to deliberately offset the nominal landing in order to get more doming reserve (the shift due to doming is always to the outside of the tube). You would do this using spoiler magnets put in the right places.

Permanently setting the contrast lower is not a real cure because the customer might not like such a dark picture. A better picture tube (Invar shadow mask) *is* a good cure (in most cases) but there is the cost price increase. (This is mainly due to the fact that Invar metal is harder to etch.)

Also see the section: Comments on color purity, set orientation, and doming.

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