Discussion in "Hardware" started by    pravin_35    Nov 20, 2010.
Mon Nov 22 2010, 12:09 PM
#11
@Pravin if your problem is not solved by repairing cable or replacing Data cable...

Then you need to Degauss of Demagnatise you CRT.......first do degaussing if still problem is there then move forward to colour section for repair....

Read this carefully.......Degaussing is very sensitive repair.......

Degaussing (demagnetizing) a CRT


Degaussing may be required if there are color purity problems with the
display. On rare occasions, there may be geometric distortion caused
by magnetic fields as well without color problems. The CRT can get
magnetized:

* if the TV or monitor is moved or even just rotated.

* if there has been a lightning strike nearby. A friend of mine
had a lightning strike near his house which produced all of the
effects of the EMP from a nuclear bomb.

* If a permanent magnet was brought near the screen (e.g., kid's
magnet or megawatt stereo speakers).

* If some piece of electrical or electronic equipment with unshielded
magnetic fields is in the vicinity of the TV or monitor.

Degaussing should be the first thing attempted whenever color
purity problems are detected. As noted below, first try the
internal degauss circuits of the TV or monitor by power cycling a few
times (on for a minute, off for 30 minutes, on for a minute, etc.)
If this does not help or does not completely cure the problem,
then you can try manually degaussing.

Commercial CRT Degaussers are available from parts distributors
like MCM Electronics and consist of a hundred or so turns of magnet wire
in a 6-12 inch coil. They include a line cord and momentary switch. You
flip on the switch, and bring the coil to within several inches of the
screen face. Then you slowly draw the center of the coil toward one edge
of the screen and trace the perimeter of the screen face. Then return to
the original position of the coil being flat against the center of the
screen. Next, slowly decrease the field to zero by backing straight up
across the room as you hold the coil. When you are farther than 5 feet
away you can release the line switch.

The key word here is ** slow **. Go too fast and you will freeze the
instantaneous intensity of the 50/60 Hz AC magnetic field variation
into the ferrous components of the CRT and may make the problem worse.

It looks really cool to do this while the CRT is powered. The kids will
love the color effects.

Bulk tape erasers, tape head degaussers, open frame transformers, and the
"[censored]-end" of a weller soldering gun can be used as CRT demagnetizers but
it just takes a little longer. (Be careful not to scratch the screen
face with anything sharp.) It is imperative to have the CRT running when
using these whimpier approaches, so that you can see where there are
still impurities. Never release the power switch until you're 4 or 5
feet away from the screen or you'll have to start over.

I've never known of anything being damaged by excess manual degaussing
though I would recommend keeping really powerful bulk tape erasers turned
degaussers a couple of inches from the CRT.

If an AC degaussing coil or substitute is unavailable, I have even done
degaussed with a permanent magnet but this is not recommended since it is more
likely to make the problem worse than better. However, if the display
is unusable as is, then using a small magnet can do no harm. (Don't use
a 20 pound speaker or magnetron magnet as you may rip the shadow mask right
out of the CRT - well at least distort it beyond repair. What I have in
mind is something about as powerful as a refrigerator magnet.)

Keep degaussing fields away from magnetic media. It is a good idea to
avoid degaussing in a room with floppies or back-up tapes. When removing
media from a room remember to check desk drawers and manuals for stray
floppies, too.

It is unlikely that you could actually affect magnetic media but better
safe than sorry. Of the devices mentioned above, only a bulk eraser or
strong permanent magnet are likely to have any effect - and then only when
at extremely close range (direct contact with media container).

All color CRTs include a built-in degaussing coil wrapped around the
perimeter of the CRT face. These are activated each time the CRT is
powered up cold by a 3 terminal thermister device or other control
circuitry. This is why it is often suggested that color purity problems
may go away "in a few days". It isn't a matter of time; it's the number
of cold power ups that causes it. It takes about 15 minutes of the power
being off for each cool down cycle. These built-in coils with thermal
control are never as effective as external coils.

See the document: " TV and Monitor CRT (Picture Tube) Information" for
some additional discussion of degaussing tools, techniques, and cautions.



How often to degauss


Some monitor manufacturers specifically warn about excessive use of degauss,
most likely as a result of overstressing components in the degauss circuitry
which are designed (cheaply) for only infrequent use. In particular,
there is often a thermister that dissipates significant power for the second
or two that the degauss is active. Also, the large coil around the CRT
is not rated for continuous operation and may overheat.

If one or two activations of the degauss button do not clear up the color
problems, manual degaussing using an external coil may be needed
or the monitor may need internal purity/color adjustments. Or, you may have
just installed your megawatt stereo speakers next to the monitor!

You should only need to degauss if you see color purity problems
on your CRT. Otherwise it is unnecessary. The reasons it only works the
first time is that the degauss timing is controlled by a termister
which heats up and cuts off the current. If you push the button
twice in a row, that thermister is still hot and so little happens.

One word of clarification: In order for the degauss operation to be
effective, the AC current in the coil must approach zero before the
circuit cuts out. The circuit to accomplish this often involves a
thermister to gradually decrease the current (over a matter of several
seconds), and in better monitors, a relay to totally cut off the current
after a certain delay. If the current was turned off suddenly, you would
likely be left with a more magnetized CRT. There are time delay elements
involved which prevent multiple degauss operations in succession. Whether
this is by design or accident, it does prevent the degauss coil - which is
usually grossly undersized for continuous operation - to cool.

 pravin_35 like this.
Mon Nov 22 2010, 06:55 PM
#12
Most monitors have a Degaussing switch,
or an option in the Setup menu.

Tue Nov 23 2010, 03:51 AM
#13
Phil I agree.... some monitors have Degaussing switch and that switch automatically degauss the CRT by switching the power ON and OFF...

in Degaussing first thing to do is to turn ON and OFF ..........ON your monitor for one minute and turn off it for 30 minutes then again ON for one minute and OFF for 30 minutes.......do this for four to five times many times problem is solved by doing this process but if this not works then u have to do Manual Degaussing.......
Tue Nov 23 2010, 06:50 PM
#14


Phil I agree.... some monitors have Degaussing switch and that switch automatically degauss the CRT by switching the power ON and OFF...

coolmirza143


I should have said "button" or menu option.
This allows you to degauss at any time without the stress (to the monitor) of switching off and on.


[ Edited Tue Nov 23 2010, 06:50 PM ]
Wed Nov 24 2010, 03:41 AM
#15


I should have said "button" or menu option.
This allows you to degauss at any time without the stress (to the monitor) of switching off and on.

ExperimenterUK



Phil i read about this somewhere before but in practical repair i never see this kind of Degaussing Switch...

here is another method that experts follow...Degaussing using Permanent Magnet...i can also degauss using this method if there is a problem in corner or small portion..... This method works but it can harm CRT in case of improper use.....

Wed Nov 24 2010, 04:23 AM
#16
hi,

i have degauss option in the menu i tried it but still my problem is not solved...........
Wed Nov 24 2010, 04:25 AM
#17
upload pics of your monitor screen display......
Sat Nov 27 2010, 08:41 AM
#18
hi guys & romel,


can u guide me for repair my monitor ....

i have given biggggggggggg shock no reaction... if i repeat do 2 or 3 times my monitor will broke

also i have checked the cable,.... no problem... i think some lizards r living inside it makes problem yesterday i seen!!!!!!!



[ Edited Sat Nov 27 2010, 08:44 AM ]
Sat Nov 27 2010, 09:18 AM
#19
hi pravin_35
lizards
then open it and clear its dust and lizards too
Sat Nov 27 2010, 09:22 AM
#20
ya sure majoka tdy i am going to do it going to do damage for lizards family...he he he he

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