NotTaR of Television Sets : Purple blob - or worse                  
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Purple blob - or worse

Have you tried demagnetizing it? Try powering it off for a half hour, then on. Repeat a couple of times. This should activate the internal degausser. See the section: Degaussing (demagnetizing) a CRT.

Is there any chance that someone waved a magnet hear the tube? Remove it and/or move any items like monster speakers away from the set.

Was your kid experimenting with nuclear explosives - an EMP would magnetize the CRT. Nearby lightning strikes may have a similar effect.

If demagnetizing does not help, then it is possible that something shifted on the CRT - there are a variety of little magnets that are stuck on at the time of manufacture to adjust purity. There are also service adjustments but it is unlikely (though not impossible) that these would have shifted suddenly. This may be a task for a service shop but you can try your hand at it if you get the Sams' Photofact or service manual - don't attempt purity adjustments without one.

If the set was dropped, then the internal shadow mask of the CRT may have become distorted or popped loose and you now have a hundred pound paper weight. See the "Sony1" and "Sony2" photos in James Sweet's Sony/Trinitron Directory for some screen shots showing the symptoms resulting from a monitor falling on its face. :( If the discoloration is slight, some carefully placed 'refrigerator' magnets around the periphery of the tube might help. See the section: Magnet fix for purity problems - if duct tape works, use it!.

It is even possible that this is a 'feature' complements of the manufacturer. If certain components like transformers and loudspeakers are of inferior design and/or are located too close to the CRT, they could have an effect on purity. Even if you did not notice the problem when the set was new, it might always have been marginal and now a discoloration is visible due to slight changes or movement of components over time.

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