"John-Del" wrote in message
...
On Sunday, June 2, 2013 1:15:58 PM UTC-4, Smarty wrote:


I have not dealt at all with magnetized Trinitrons / aperture grills,

and only have very limited experience with magnetized conventional CRTs

but purity problems certainly were visible in the black and white images

of those needing degaussing. It did not take moving color images to

suggest purity / magnetization nor did it take careful inspection.


Perhaps your experience is with the old delta gun arrangement, which were
prone to more purity error and more severe error. But I can tell you that
with modern in line arrangements (Sony being no exception), bad purity is
not always obvious in black and white pictures.

+1 - see below


The

other, even more confusing original post issue was the non stationary

nature of the color shifts, and the fact they were reported as moving

with the displayed image, again evidence that the problem was not a

purity problem.



I reread the OP's post several times, and don't see what you mean by non
stationary color shift. From what I read, the purity error was static on
the screen. I'm not a betting man, but I'd bet that if the OP degausses
the TV, the problem will go away.


Yes. I couldn't see where he said that it was a shifting problem, either. I
have seen shifting purity errors, where the shadowmask has become detached
from its frame at one or more of the spot welds. Localised heating from high
luminance areas of the picture can then cause the shadowmask to expand
non-linearly and distort at the point of detachment, resulting in severe,
and non-constant purity errors. On more than one occasion, I have seen a
sort of 'strobing' purity error like a kaleidoscope pattern, as a detached
shadowmask heats and 'pings' and then cools back and then does it again and
so on.

As to purity errors being visible on black and white pictures, other than
the fact that the the phosphors have different efficiencies, and the drive
levels are different for assorted reasons, it doesn't actually matter that
much that the phosphors are being excited by the 'wrong' beams. The mix will
still make something that approximates to white - or shades of grey -
sufficiently well for it not to be glaringly obvious. More a sort of 'dirty
patch' on the picture. However, as soon as a colour picture is viewed on the
same gaussed up CRT, the error is immediately visible

Arfa