MadSci Network: Engineering

Re: What does the degauss button on my monitor do?

Date: Mon Apr 23 14:37:48 2001
Posted By: Valdis Kletnieks, Staff, Computing Center, Virginia Tech Computing Center
Area of science: Engineering
ID: 987626292.Eg

Most monitors are basically just television displays on steroids.  Other
than the average TV displaying only a 680x480 or so maximum resolution, and
not as many rescans/second, the basic technology is the same - have a hot
wire at the back of the monitor throwing off electrons, accellerate them
towards the front by applying a voltage, and steer the beam across the
screen, line by line, using electromagnets.  However, when you're looking
at a 27 inch television, and only 680x480 tops (and probably more like
500x400 in practice),  the aim you need isn't that crucial - I actually
checked my Magnavox TV, and you can *see* the little red/green/blue dots
quite easily  - they're on the order of 1/32 of an inch (about 0.8 mm) in size.

On the other hand, if you try to put 1280x1024 on a 17" screen, you'll see
that the aim you need is *much* higher - on the order of 1/128th of an
inch, or 0.2mm (which is where the "screen pitch" of a monitor comes from).
The tighter tolerances for all this is what drives the price of a Really
Good monitor up so high.  And of course, the closer to the ragged edge your
technology is running, the more things can go wrong.

One thing that can go wrong is that the "mask" at the front of the monitor
can become magnetized or aquire a residual charge - a common cause of this
is using unshielded speakers next to the monitor (speakers designed for
computer use are shielded so the magnets in the speakers don't interfere
with a monitor/whatever nearby).  If the mask gets magnetized, it will (a)
warp slightly and (b) cause electrons to swerve slightly.  The combined
effect is that the color balance will be "off" on part of the screen.

I actually had this happen to a monitor once - a regular audio speaker
ended up against the monitor face for a few seconds, and for *months*
afterward, there was a circle in that corner of the face where the color
was too green, surrounded by a field that was too purple.

The 'degauss' circuit in your monitor sends a burst of energy across the
mask, and hopefully de-magnetizes it.  Many modern monitors automatically
degauss when you turn them on.  If yours doesn't, you should manually hit
the 'degauss' button once in a while (once a month or so) if things are
starting to get fuzzy or tinged wtih wrong colors.  It won't hurt your
monitor to do it occasionally, and may fix the image quality.

If the image quality doesn't improve, either the problem is something else,
or the mask is too magnetized for the degausser to fix.

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