ric said:
the earth's magnetic field makes bugger all difference to TFTs.
it DOES however, make a difference to CRTs and some TVs.
to prove this, if you've a big, preferably fairly high-res monitor,
turn it through 180 degrees without turning it off/on and degaussing,
and look closely at the screen. a slight colour stain is very common,
which'll usually clear by the automatic degauss.
it doesn't always, but can be done manually using a, well, manual
degausser - which is a big circular electromagnet that you turn on
about 6 foot from the screen, bring it towards it and wipe around the
outside of the casing, before retiring to a slight distance and turning
it off.
anyone who's spent any time in the TV repair business will know what i
mean - usually severe cases are caused by non-shielded loudspeakers
placed too close to the TV...
Ahhh, yes, the de-gauss wand. Been known to wipe credit cards, especially
when used as an offensive weapon or as weapon against an offensive person.
Been there, done that....
You are correct quite about the earth's magnetic field affecting CRT
monitors and TVs. Normally, when the TV/CRTs are shifted from one location
to another that they face 180° in the opposite direction, you will notice
some colour bleed because the mask screen has been magnetised to the
previous location. The longer it was sitting in the original location, the
more obvious the bleed when the orientation is changed.
If you have an old monitor, store it on its side or upside down for at least
6 months and then re-test. I can guarantee you will see colour bleed when
reconnected. If it is old, it could take more than 10 power cycles for the
in-built de-gausser to fix the screen, assuming it has a de-gausser and it
works. The wand makes the fix much faster.
Dave
PS. By wand, the one I use is an electro-magnet mounted in one end of 3" dia
(7.5cm) poly pipe, about 18" (45cm) long and has a press-switch on the other
end. It only has about a 25% duty cycle but since it was free, I can't
complain!