TV TECHNICAL QUESTION

Discussion in 'DVD Video' started by PW, Dec 21, 2003.

  1. PW

    PW Guest

    Just wanted to ask:

    I have an old 27" TV that has seen better days, in particular
    the color is messed up in some spots, i.e. blue blotches in the
    corner, etc...

    I just wanted to know if these degaussing coils I've seen
    actually work. I have a brand new TV to watch my movies on,
    but I didn't want to throw this old TV away, so if I can get
    one of these coils and restore the color....and I wanted
    to know if anyone has used the coils.

    Do they work? Are they worth it? And where are the
    best places to get them? Are they only available online
    or can you get them in stores?

    Thanks for any help.
    PW, Dec 21, 2003
    #1
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  2. PW

    John Savard Guest

    On 20 Dec 2003 16:07:33 -0800, (PW) wrote,
    in part:

    >Do they work? Are they worth it?


    A degaussing coil is usually a tool in a TV repairman's toolkit, not
    something that a TV set owner needs to own.

    Yes, they do work, if that's what the problem is. TV picture tubes
    work by sending electrons out to hit colored phosphor dots on the
    screen, and moving electrons will have their paths bent by stray
    magnetic fields. This can bend the electron's path after the shadow
    mask, causing electrons to hit the dots of the wrong color.

    What you have to do to demagnetise the shadow mask with a degaussing
    coil is to very slowly and gradually move it away from the screen as
    you wave it around; used wrong, it can make much stronger magnetic
    fields than were there before, making things worse.

    John Savard
    http://home.ecn.ab.ca/~jsavard/index.html
    John Savard, Dec 21, 2003
    #2
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  3. On 20 Dec 2003 16:07:33 -0800, (PW) wrote:

    >Just wanted to ask:
    >
    >I have an old 27" TV that has seen better days, in particular
    >the color is messed up in some spots, i.e. blue blotches in the
    >corner, etc...
    >
    >I just wanted to know if these degaussing coils I've seen
    >actually work. I have a brand new TV to watch my movies on,
    >but I didn't want to throw this old TV away, so if I can get
    >one of these coils and restore the color....and I wanted
    >to know if anyone has used the coils.
    >
    >Do they work? Are they worth it? And where are the
    >best places to get them? Are they only available online
    >or can you get them in stores?
    >
    >Thanks for any help.



    Oh yes, CRT degaussing coils are certainly effective. The best place
    to buy them seems to be electronics parts stores, look under
    "Electronics, distributor and retail" in your Yellow Pages.

    As an alternative you might have a handheld cassette tape eraser,
    waving that around right in front of the picture tube will do a fairly
    good job, though not as good as the deqaussing coil.

    But first, try to determine WHY the the tube is magnetized! Maybe
    there are, or were, unshielded loudspeakers close by the set. Look
    for anything magnetized in the vicinity of the TV. (This is SO often
    overlooked!) Removing the source of the magnetism will mostly let the
    CRT restore to a neutral state. Also try turning the TV in a
    different direction, since the earth's Magnetic field is strong enough
    to affect some TV's that are in precisely the wrong direction.
    Another possibility is that the yoke has slipped, thus affecting beam
    landing, or if the tube and yoke are a bit out of manufacturing
    tolerance one or more spot purity disc magnets may have been needed,
    and it(they) may have fallen off.

    .. Steve .
    Steve(JazzHunter), Dec 21, 2003
    #3
  4. PW

    fred Guest

    > >I have an old 27" TV that has seen better days, in particular
    > >the color is messed up in some spots, i.e. blue blotches in the
    > >corner, etc...
    > >
    > >I just wanted to know if these degaussing coils I've seen
    > >actually work. I have a brand new TV to watch my movies on,
    > >but I didn't want to throw this old TV away, so if I can get
    > >one of these coils and restore the color....and I wanted
    > >to know if anyone has used the coils.
    > >
    > >Do they work? Are they worth it? And where are the
    > >best places to get them? Are they only available online
    > >or can you get them in stores?


    I use a common Radio Shack bulk tape eraser and it works great. Set
    must be on, and you have to power it up from several feet away and
    approach the set slowly, and don't go so close that you make contact with
    the set, you can see what you are doing on the screen and just need to go
    across the whole screen slowly then back away slowly and don't turn it off
    until you are several feet away. If this is an old set anyway, go ahead
    and try it out. If you don't get the colored areas out, you can try it
    again until you get it right.

    > Oh yes, CRT degaussing coils are certainly effective. The best place
    > to buy them seems to be electronics parts stores, look under
    > "Electronics, distributor and retail" in your Yellow Pages.


    God only knows how much they charge for one of those, the bulk tape eraser
    at Radio Shack works just fine, I know, that is what I use.

    > As an alternative you might have a handheld cassette tape eraser,
    > waving that around right in front of the picture tube will do a fairly
    > good job, though not as good as the deqaussing coil.


    It does a terrific job. More than enough power. I have fixed several
    sets with one.

    > But first, try to determine WHY the the tube is magnetized! Maybe
    > there are, or were, unshielded loudspeakers close by the set. Look
    > for anything magnetized in the vicinity of the TV. (This is SO often
    > overlooked!) Removing the source of the magnetism will mostly let the
    > CRT restore to a neutral state.


    Wrong, taking a magnet away will not restore the screen, it will stay that
    way until you fix it. Sometimes, if it was just a small magnet, after
    turning the set on a few times, the built in degaussing coil might fix it,
    but this is very rare.

    > Also try turning the TV in a
    > different direction, since the earth's Magnetic field is strong enough
    > to affect some TV's that are in precisely the wrong direction.


    Old wives tale. Get the bulk tape eraser, magic and witchcraft won't
    fix it.

    > Another possibility is that the yoke has slipped, thus affecting beam
    > landing, or if the tube and yoke are a bit out of manufacturing
    > tolerance one or more spot purity disc magnets may have been needed,
    > and it(they) may have fallen off.


    Then you will have a convergence problem, not the same symptoms.
    fred, Dec 21, 2003
    #4
  5. On Sun, 21 Dec 2003 06:57:01 GMT, fred <> wrote:

    >> >I have an old 27" TV that has seen better days, in particular
    >> >the color is messed up in some spots, i.e. blue blotches in the
    >> >corner, etc...
    >> >

    >
    >
    >> Oh yes, CRT degaussing coils are certainly effective. The best place
    >> to buy them seems to be electronics parts stores, look under
    >> "Electronics, distributor and retail" in your Yellow Pages.

    >
    >God only knows how much they charge for one of those, the bulk tape eraser
    >at Radio Shack works just fine, I know, that is what I use.


    A local parts store charges $16 CDN.
    >
    >> As an alternative you might have a handheld cassette tape eraser,
    >> waving that around right in front of the picture tube will do a fairly
    >> good job, though not as good as the deqaussing coil.

    >
    >It does a terrific job. More than enough power. I have fixed several
    >sets with one.


    Still not as good as the proper coil. It can't get rid of any
    magnetic bias on the Bell or mounting hardware.
    >
    >> But first, try to determine WHY the the tube is magnetized! Maybe
    >> there are, or were, unshielded loudspeakers close by the set. Look
    >> for anything magnetized in the vicinity of the TV. (This is SO often
    >> overlooked!) Removing the source of the magnetism will mostly let the
    >> CRT restore to a neutral state.

    >
    >Wrong, taking a magnet away will not restore the screen, it will stay that
    >way until you fix it. Sometimes, if it was just a small magnet, after
    >turning the set on a few times, the built in degaussing coil might fix it,
    >but this is very rare.


    Look, I have been a technician forr 30 years. I have worked on TV's
    since they were just about all tube-types. Don't tell me that 30
    years of experience is "wrong." Not only does the built-in coil often
    remove the effect of temporary magnetism, but the actual heating and
    cooling of the mask plus the discharge of electron beam scanning also
    wipes out the magnetism, or at least biases it a certain way. It is
    most important that CURRENT, existing, sources of magnetism be removed
    before attempting degaussing, which may not be necessary after all.
    In other words the internal degaussing of this 27" set may not be able
    to do its job because of a close-by speaker etc.
    >
    >> Also try turning the TV in a
    >> different direction, since the earth's Magnetic field is strong enough
    >> to affect some TV's that are in precisely the wrong direction.

    >
    >Old wives tale. Get the bulk tape eraser, magic and witchcraft won't
    >fix it.


    Again it is NOT an "Old Wives Tale!" the Earth's magnetic field has a
    profound effect on bean landng, why do you think the shield is there?
    Many monitors and TV's above a certain size have a built-in Earth's
    magnetic field detector that controls a circuit that provides a small
    current to a coil around the neck or bell to counteract the field.
    The earth's field has been the bane of colour CRT designers since the
    beginning. The set's degaussing coil is mainly there to wipe out
    magnetism that has built up on the tube while the set was off and
    cool.
    >
    >> Another possibility is that the yoke has slipped, thus affecting beam
    >> landing, or if the tube and yoke are a bit out of manufacturing
    >> tolerance one or more spot purity disc magnets may have been needed,
    >> and it(they) may have fallen off.

    >
    >Then you will have a convergence problem, not the same symptoms.


    No, slipping backwards slightly (which is unlikely, but I have seen
    this) will change the crossover point of the beams and therefore beam
    landing much more than overall divergence of the beams. In other
    words any increased misconvergence is completely masked by the
    splotches of impurity. You can move the yoke 1/2" back and forth on a
    set with the rings mounted separately and the convergence remains
    almost spot on, while the purity goes shot to hell. Slippage of the
    rings on the neck on newer sets or shifting of waveform voltages on
    the convergence coils of triad CRTs is what matters for convergence.
    Sliding the yoke back and forth ONLY affects purity. Tilting up and
    down affects corner purity a little and convergence just at the centre
    right and left sides.

    . Steve .
    >
    Steve(JazzHunter), Dec 21, 2003
    #5
  6. PW

    Larry Lynch Guest

    In article <>,
    says...
    > Old wives tale. Get the bulk tape eraser, magic and witchcraft won't
    > fix it.
    >


    Sadly, NOT an old wives tale.. Just not true of mosr
    MODERN Televisions.

    Early color TV used a big ROUND faced jug and long deep
    METAL body with a plastic mask to shape the picture and.

    These "jugs" were so sensitive to magnetic fields that
    the wiring in the house walls could, and did screw up
    the picture.

    Most of the time if the set was moved from one room to
    another, the "Jug" would need degausing.

    I still have a 1960's vintage degaussing coil. It is
    about 12" in diameter, and about 3/4" thick.

    This coil was passed around both SIDES of the old TVs in
    a slow circular motion before moving to the face of the
    CRT (never stopping the circular motion) then passed
    several times across the face of the tube before SLOWLY
    backing away from the set (still maintaining the
    circular motion). When about three feet from the face of
    the tube you turn the EDGE of the coil toward the face
    of the screen and switch off the coil.

    Most of the time, no adjustment was needed INSIDE the
    old sets unless the set had been moved from house to
    house, being subject to the vibration of truck
    transport. Vibration could, and would, move the "purity
    rings" and other such stuff on the neck of the tube.

    Through the 60's 70's and 80's CRT development pretty
    much made the users of degaussing coils an extinct
    species.

    YES! if you have a LARGE STRONG hand held Tape eraser
    (Like the one Radio Shack used to sell) you stand a very
    good chance of being able to clear up the problem as
    long as its source is gone or removed (un-shielded
    speakers ect. near the set).

    I do, however, recommend that you use the afore-
    mentioned technique (starting with the SIDES ect) to be
    sure you do the best job you can.

    Since you cant accomplish much by turning the tape
    eraser edgewise at the end of the pass (the field is to
    small and concentrated) just move it as far away as
    possible before switching off.


    --
    Larry Lynch
    Lasting Imagery
    Mystic, Ct.
    Larry Lynch, Dec 21, 2003
    #6
  7. PW

    Larry Lynch Guest

    In article <>,
    says...
    > No, slipping backwards slightly (which is unlikely, but I have seen
    > this) will change the crossover point of the beams and therefore beam
    > landing much more than overall divergence of the beams. In other
    > words any increased misconvergence is completely masked by the
    > splotches of impurity. You can move the yoke 1/2" back and forth on a
    > set with the rings mounted separately and the convergence remains
    > almost spot on, while the purity goes shot to hell. Slippage of the
    > rings on the neck on newer sets or shifting of waveform voltages on
    > the convergence coils of triad CRTs is what matters for convergence.
    > Sliding the yoke back and forth ONLY affects purity. Tilting up and
    > down affects corner purity a little and convergence just at the centre
    > right and left sides.
    >
    > . Steve .
    >

    I wish I had read your post before posting mine!!!
    You were so much more concise
    --
    Larry Lynch
    Lasting Imagery
    Mystic, Ct.
    Larry Lynch, Dec 21, 2003
    #7
  8. On Sun, 21 Dec 2003 07:17:52 -0500, Larry Lynch
    <> wrote:

    >In article <>,
    > says...
    >> No, slipping backwards slightly (which is unlikely, but I have seen
    >> this) will change the crossover point of the beams and therefore beam
    >> landing much more than overall divergence of the beams. In other
    >> words any increased misconvergence is completely masked by the
    >> splotches of impurity. You can move the yoke 1/2" back and forth on a
    >> set with the rings mounted separately and the convergence remains
    >> almost spot on, while the purity goes shot to hell. Slippage of the
    >> rings on the neck on newer sets or shifting of waveform voltages on
    >> the convergence coils of triad CRTs is what matters for convergence.
    >> Sliding the yoke back and forth ONLY affects purity. Tilting up and
    >> down affects corner purity a little and convergence just at the centre
    >> right and left sides.
    >>
    >> . Steve .
    >>

    >I wish I had read your post before posting mine!!!
    >You were so much more concise


    Your comments were a different viewpoint and separated out the
    differences between new and old TV's, so it was a completely valid and
    interesting post.

    .. Steve .
    Steve(JazzHunter), Dec 21, 2003
    #8
  9. PW

    Larry Lynch Guest

    In article <>,
    says...
    > Your comments were a different viewpoint and separated out the
    > differences between new and old TV's, so it was a completely valid and
    > interesting post.
    >
    > . Steve
    >


    Thanks!

    Sometimes being an "old codger" helps with stuff.
    --
    Larry Lynch
    Lasting Imagery
    Mystic, Ct.
    Larry Lynch, Dec 21, 2003
    #9
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