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Okay, basically the way old school monitors and television sets work is that they have a
cathode ray tube, or CRT inside.
An electron beam from the back shoots electrons to the front
where they're displayed back and forth across the screen to create a picture.
Now these electron beams can be deflected by
magnetic fields. To prove that I've got a small fridge magnet here,
and you can see as I move the magnet round and round the screen
I'm deflecting, and actually changing and modifying the image because
the electron beam going to the front is being deflected by
strong magnetic fields. That's a black and white set.
You can do the same thing with a colour television set. Because there are three beams
one for red, one for blue and one for green information, I'm going to deflect all three.
And see what happens. You get these wonderful wonderful
spiral rainbow patterns
because the beams are being deflected in such a way
that they deflect onto dots that they're not supposed to hit.
And so you get colours that are unnatural, sort of rainbow-like.
The moment you take away the magnet, everything's totally fine again.
Oops.
So how do you fix this problem?
What I have here is an old CRT-based color television set
that's suffering from what we call purity error. The colours are not the same
from one side of the screen to the other. Or top to bottom. They're not
where they're supposed to be.
The way to fix that, because I have magnetized the shadow mask
with my fridge magnet is to use what's called
a "degaussing coil." Here's one right here. It's very simple. You plug it into the wall
it's got a power switch on the side. And it's just great big coil of wire.
When I turn this thing on, it generates
alternating magnetic fields back and forth, back and forth, sixty times a second.
Because I plugged into alternating current in the wall socket.
It works like this. You turn it on, and when I put it close to the monitor
you can see some patterns forming. And slowly slowly surely
you move it backwards just a little at a time a little step at a time.
Eventually if you move it back far enough, you get to the point
where you can turn off the degaussing coil
and miracle of miracles, you've got a fixed TV set.
You got rid of the purity error.