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It is largely a function of the precision wound deflection yoke that is
carefully matched to the CRT at the factory. This yoke requires only basic
static convergence to be adjusted, and this is accomplished usually with a
combination of 4 and 6 pole annular magnets at the rear of the yoke. See
second para from bottom
http://www.answers.com/topic/television-receiver-1?cat=technology
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I have.
There's also the issue of focus. I've seen CRTs go "soft" as they age.
Focus is not an issue on flat panels.
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It is fairly rare for CRTs to age this way these days. Often, something else
in the circuitry fails, to render the monitor not worth repairing, before
the CRT is showing serious signs of aging, although I do accept that this is
a potential age-related failure mode of a CRT display. Whilst I agree that
focus per se is not an issue that can be directly related to LCD display
technology, many cheap end displays never-the-less do not look as sharp as a
*good* CRT display, and also suffer from serious motion blur, both as a
result of switching lag in the LCD cells, and display drive circuitry. There
are other issues with LCD monitors, which some consider to be a bigger
problem than the minor defects with CRT display technology. These include
poor contrast ratio, poor eveness of the back illumination, fairly rapid
wearing of the CCFLs providing that illumination, very poor results with a
drive source resolution of anything other than the panel's native figure,
and motion blur as already discussed.
Focus of modern CRTs is well taken care of. Very well performing dynamic
focus circuits have been in common usage for some years now, and the CRTs
electron lenses are carefully designed to maximise the beneficial effects of
this. Again, some cheap end monitors / TV sets are not terribly good in this
respect, but that is more of a cost than technology issue. On a decent
quality CRT display, you would be fairly hard pressed to find focus errors
worth complaining about.
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Then there's magnetic effects. Aside from degaussing, which modern CRTs
are designed to do automatically, you have to worry about external fields,
such as from nearby loudspeakers. I had a modern CRT image start to
"shimmy" when an outdoor security light came on every evening. Flat
panels are immune to external magnetic fields and don't need degaussing.
*************
Magnetic effects should not be an issue with modern CRTs, unless a powerful
field is brought close to the face of the CRT. The construction of the
device includes a magnetic shield, and before they did, they were surrounded
by a mu-metal shield, which blocked all but the strongest interfering
fields. It is not the CRT which degauses itself automatically. Rather, it is
a piece of circuitry which at switch on, applies an initially large,
progressively decaying, AC current to the degausing coils surrounding the
CRT. In the case of a TV set, that's it, but with a computer monitor, as
well as this automatic degausing at switch on, a manual switch or menu
option is often provided as well, to allow for a 'hot' demagnetisation. I've
never really understood why manufacturers thought this necessary. Maybe
because monitors are mounted on a tilt and swivel base, which could result
in purity errors due to the realignment of the earth's magnetic field if you
do spin the monitor round, but it would have gone back right anyway, when
you turned it back. Still, it looks pretty, if you're bored with what you're
doing ...
As far as your monitor shimmering when the outside light came on, I would
suggest that this was nothing to do with magnetic fields or CRT technology.
Far more likely to be mains-borne mutual interference between the monitor's
switch mode power supply, and something like triac switching in the outside
light. Did you ever pin down what you thought was actually causing the
problem ?
Arfa
