B
bob
I was playing around with a magnet on my CRT screen. Now my monitor
has some dark patches. Any way to fix this?
has some dark patches. Any way to fix this?
R
Rod Speed
Buy a new monitor.
P
paulmd
1) Degauss button. If it's bad, it'll take a few tries. Sometimes the
degauss is automatic on monitor power on, sometimes it's buried in the
menu, sometimes there's a button. Just depends on your monitor.
2) manual degausser. If it's really bad, and the degaussing isn't
helping.
3) stop screwing with magnents.
P
Paul
A monitor has a built-in degaussing coil, and it applies an
A.C. magnetic field, to try to erase residual magnetism in
the monitor. That is enough to correct for small magnetic
anomalies.
Placing a magnet on a monitor, can magnetize the metal frame
of the monitor. The built-in degaussing coil is neither powerful
enough, nor positioned well enough, to correct magnetic vandalism
of this kind.
When I bought a new CRT 10 years ago, the brand new CRT had
discoloration typical of a magnetization problem. I took the
monitor to a TV repair shop at a larger TV/Stereo store, and
they used a portable degaussing coil. The coil is about one
foot in diameter. The service person waves the coil around
the monitor and steps way back from the monitor before
turning it off. Since the magnetic field lines point out
of the hole in the middle of the coil, just before the service
person turns off the coil, they turn it so the opening in the
coil is no longer pointing at the CRT. That prevents the spike
when the AC switch on the degaussing coil is turned off,
from polluting the monitor again with magnetism.
One treatment seemed to fix up my new monitor, so it had
a nice white background when the picture was supposed to
be white.
Keep all magnets away from the CRT, if you expect to keep
your color purity. The degaussing built into the monitor
is enough to keep it clean, unless you stick a magnet on
your screen or on the side where some framework metal is
located. And since we know the magnet you used, came out
of that disk drive you were playing with, that is about
the strongest small magnet you could have selected for
the job
The TV/Stereo store I used, did my degaussing for free,
but I'm sure most businesses would charge for the service.
Even though it only takes about 2 minutes to do. Note
that there are no guarantees with the portable degausser -
a determined vandal with a magnet can permanently ruin a
monitor, if the applied field was strong enough. Even the
portable degausser has a limited ability to erase
magnetism in the frame of the monitor. If you were thinking
of moving up to a 5 lb alnico magnet for your next
experiment, think again
(some magnets to keep away from your monitor or TV set)
http://scientificsonline.com/product.asp_Q_pn_E_3041946
Paul
M
Mike Walsh
[email protected] said:
A bulk tape eraser will work.
K
kony
You have caused a glitch in the matrix. The only solution
is now to have your other world double, stand in front of
their monitor with the magnet flipped the other way around
and play with it at the exact same time you did. So of
course, you will have to find a way to get a time machine to
your other world double so they are ready when you did it
the first time.
Most people find this cost prohibitive and just turn their
monitor on and off a few times.
M
meow2222
kony said:
but that can sometimes go horribly wrong. The unfortunate result is
known as roddism.
Recommend turning off the power when not in use, otherwise people will
on/off it relatively rapidly, which wont work. The theremistors need 10
mins+ to cool between onoffs.
NT
V
Vanguard
Mike Walsh said:
Depends on the CRT monitor (which would be affected by the magnet
which induced the dark spots on the OP's monitor). If it uses a
shadow mask, using an electromagnetic degausser or bulk eraser will
permanently deform the shadow mask and ruin the monitor. The shadow
mask is a metal plate with holes that align with the phosphor groups.
It is an aperture grill to keep the electron beams from straying onto
other phosphor groups. A slight variance in its position will severely
degrade usability of the screen. An electromagnetic degausser,
especially like a bulk tape eraser, is far too strong to be using on
monitors. Rather than simply get rid of stray magnetic charges that
affect the electron beam, the strong degausser (hand-held or bulk
eraser) may end up flexing the shadow mask and screw up its
positioning.
While you can use the hand-held degausser or bulk tape eraser to
degauss a monitor or television, start several feet AWAY before
flipping on the switch. Start a few feet away, turn on, and approach
to see when there is some effect. Then try getting rid of the spots
at the farthest distance away that will have any effect (you can
usually see the color pattern and see if there is any effect on the
dark spot).
Most monitors already have a degaussing circuit, so just repeatedly
turn on and off the monitor to activate it over and over. If it
doesn't work, it is likely you will need to get too close with the
external degaussers to effect a change without also distorting the
shadow mask, if there is one.
http://www.anatekcorp.com/smask.htm
http://www.wikihow.com/Degauss-a-Computer-Monitor
M
meow2222
ohh, is that how to make a psychedelic monitor?
NT
D
Davy
As suggested, try a degaussing coil, these are like a wand that you
plug in to the mains and move slowly across the screen, moving away
several feet before switching the coil off.
Normally there is a demagnitizing coil fitted around the screen of a
CRT display, when you switch on a large current flows through it
until a Posistor (a negative and posistive co-efficient thermistor)
heats up, the resistance rises thus cutting the current off.
Sometimes, leaving the set switched off for a couple of hours and
switching it back on will do the trick - the secret is letting the
Posistor to cool down as these things run warm when the monitor is
switched on.
I have de-magnitised many a TV set with the ol' soldering gun.... no,
no not a soldering iron. The soldering gun uses a 'U' shaped copper
tip and the heat is produced by electro magnetism, the heat is
produced by 'eddy currents' and not by a heating elemint like a
standard soldering iron.
Again, before switching the iron off move at least a foot or so away
from the screen. During the process you will see coloured parterns
waving across the screen.
Sometimes the shadow mask is permanently destroyed or can become
distorted making the tube useless.
Davy
plug in to the mains and move slowly across the screen, moving away
several feet before switching the coil off.
Normally there is a demagnitizing coil fitted around the screen of a
CRT display, when you switch on a large current flows through it
until a Posistor (a negative and posistive co-efficient thermistor)
heats up, the resistance rises thus cutting the current off.
Sometimes, leaving the set switched off for a couple of hours and
switching it back on will do the trick - the secret is letting the
Posistor to cool down as these things run warm when the monitor is
switched on.
I have de-magnitised many a TV set with the ol' soldering gun.... no,
no not a soldering iron. The soldering gun uses a 'U' shaped copper
tip and the heat is produced by electro magnetism, the heat is
produced by 'eddy currents' and not by a heating elemint like a
standard soldering iron.
Again, before switching the iron off move at least a foot or so away
from the screen. During the process you will see coloured parterns
waving across the screen.
Sometimes the shadow mask is permanently destroyed or can become
distorted making the tube useless.
Davy
M
Mike Walsh
The magnetic field of my bulk tape eraser is indeed very strong. I have never had to use it on a high quality monitor. I have used it on a couple of TVs and cheap computer monitors that apparently had weak degaussing coils, and did not have to get very close for it to do the job.
D
DaveW
You can TRY "degaussing" the screen to remove the latent magnetism.
V
Vanguard
Mike Walsh said:
--- REPLY SEPARATOR ---
That's why I suggest starting several feet away from the CRT to see
when it starts having effect, and then try correcting the problem at
that distance, moving only closer if there is no permanent effect. In
fact, in one of the articles that I mentioned, they use the trick of
moving the backend of a soldering iron around with its weak field to
work over the problem area.
K
kony
It should be noted that to use a soldering iron you have to
use the type with the transformer in the body of the iron,
one of the larger gun types as the smaller gun or pencil
types will not work- don't generate much if any magnetic
field in the iron themselves (though some do in the base
station, if/when it has a base station).