CRT Teardown

Discussion in 'General Electronics Chat' started by Georacer, Sep 17, 2013.

  1. Georacer

    Thread Starter Moderator

    Nov 25, 2009
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    Hey everybody,

    I just took apart an old CRT TV (younger than me) and from the inside of the frame, around the tube/screen, there was a thick loop of wire. It was connected to the board, but not directly to any supply, if I traced it correctly.

    Does anybody have any idea what this was for?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Degaussing coil?
     
  3. #12

    Expert

    Nov 30, 2010
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    Yes. Degaussing coil. It is controlled by 2 thermistors. One is PTC, the other is NTC. Each the size of an American nickel. Each showing signs of heat.
     
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  4. Georacer

    Thread Starter Moderator

    Nov 25, 2009
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    Thanks.

    I found this over at Wikipedia:
    If this is true, then why is an NTC Thermistor used as well?
     
  5. #12

    Expert

    Nov 30, 2010
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    Series/shunt. One in series limits the current as it heats up, the other shunts the small remaining current after the limiter heats up and fails to completely stop all current.
     
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  6. Georacer

    Thread Starter Moderator

    Nov 25, 2009
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    Nice. As Destin says, "smarter every day".
     
  7. #12

    Expert

    Nov 30, 2010
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    As #12 says, "I learn something almost every day on this site".

    Anyway, happy to be an old TV guy that can explain extinct appliances.
     
  8. sheldons

    Well-Known Member

    Oct 26, 2011
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    that is the degaussing coil-on switch on it is pulsed to demagnetize the viewing area on the screen ....sometimes the ptc is responsible for a set being dead due to it blowing the mains fuse on switch on,they do tend to rattle a bit when you shake them if you have a faulty one.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Most TV technicians also carried a degaussing coil with them, for manually D.G.'ing , consisted of a ~18" dia coil of wire and would be plugged int the nearest AC socket.
    I have seen it where someone doing the housekeeping uses the vacuum cleaner under the TV stand and happen to turn it off when under the set, and this can leave a nice pattern when the set is turned on which the degaussing coil does not eliminate fully.
    It temporarily magnetizes a screen in front of the CRT called a shadow mask deflecting the 3 primary colour beams .
    No longer happens with the LCD/LED sets.
    Max.
     
  10. #12

    Expert

    Nov 30, 2010
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    I still have mine.:p

    But then, I still have a CRT television that works.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I just threw one in the garbage, 21st century and all that.. Hrumph ;)
    Max.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Haha, I'm watching one right now, and I'm still in a project to repair one for my daughter. It's not going well.

    Where I live, you have to pay to throw them away.
     
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