flyback transformer wire

Discussion in 'General Electronics Chat' started by mrel, Jul 4, 2015.

  1. mrel

    Thread Starter Active Member

    Jan 20, 2009
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    Hello
    Rca television model 20f420t ,what cause red wire that come from flyback transformer to the Cathode ray tube to have arc spark jump from the red wire to cathode ray tube outside body of the tube.
    I wrap the red wire that carry 20000 volts with electrical tape the spark still jump from tape to body of the cathode ray tube.
    The arc spark jump from 20000 volts wire to cathode ray tube body than television shut down.
    Does that mean televison flyback transformer put out to much voltage is that why voltage is jump out of the high voltage wire or is just wire have bad insulated covering.
    If it just insulated covering,what to use to cover wire where the sparkis is jumping.
    mrel
     
  2. #12

    Expert

    Nov 30, 2010
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    It's bad insulation. Best to replace the wire. 20KV is insanely difficult to patch up, especially after years of carbon based dust getting on everything in the back of the TV. Silicone caulk might work...and it might not.

    ps, be careful you don't get knocked silly. The picture tube can recover enough voltage to hurt you several minutes after you discharge it.
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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  4. DickCappels

    Moderator

    Aug 21, 2008
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    Good advice. I would like to build on the note about the CRT storing enough of a charge to hurt you badly. While talking my boss gestured toward the anode cap of a color CRT that had laid on the bench for several months. I warned him to not touch it, he said "You mean this...Yow!" It can hurt you months or years later.
     
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  5. Hypatia's Protege

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    Especially when the shock results in a dropped tube!:eek:
     
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  6. ian field

    Distinguished Member

    Oct 27, 2012
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    What I used to do is clean everything with cellulose thinners - but don't get it on the flyback transformer casing as its usually ABS.

    Once its clean, silicon rubber bath sealer works well, you can get a builders cartridge of it fairly cheap from the builders yard, alternatively a tube of instant gasket from the car spares place, but less goo for more money.

    The RTV silicone sealants give off acetic acid (vinegar) as they cure - Dow Corning make a similar product that's safe on copper wiring, but if you're only using it to seal insulation and contact with copper wire is minimal, there shouldn't be a problem.
     
  7. #12

    Expert

    Nov 30, 2010
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    Need to clarify. I meant that the CRT will re-develop a dangerous voltage in only a few minutes, but it will hold that charge for weeks or months, and re-develop a voltage even after two or three discharges. You can't assume it is safe for half an hour, or even 5 minutes, after you discharge it. Simply never assume the anode can't bite you. If my words don't convince you, go touch one. You will be convinced!
     
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  8. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    In my experience such compounds remain slightly 'conductive' following curing (owing to residual electrolytes) -- granted, my experience in this regard has been in the 100kV+ 'area', still......?

    Indeed, the (organo)polysiloxane (and, hence, non-corrosive, non electrolytic) chemistry of said compounds 'makes them' a superior all-around choice for electronics applications....

    Here's an example of a source for small quantities (of equivalent product):
    http://www.alliedelec.com/gc-electronics-19-155/70159837/

    Best regards and good luck!
    HP
     
    Last edited: Jul 5, 2015
  9. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Thank you for drawing attention to this woefully under-appreciated point!

    I wish to add my 'voice' to @#12 's --- Dielectric absorption is a very real, thoroughly documented/studied phenomenon! Moreover it is not a 'freak' occurrence, but, rather, a fundamental property of electrostatics (CIP capacitors) -- IOW it 'happens' every time...

    Best regards
    HP
     
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  10. Robert Schaaf

    New Member

    Jul 5, 2015
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    I like the replies I've seen but everyone seems to forget that in those tv sets if the B+ voltage (120 volts dc) isn't regulating right and has gone up to 135 or so then you will definitely get arcing from the 2nd anode wire going to the CRT. As far as the silicone seal solution that always works (almost) Use Clear, not black then let it dry for 24 hours before firing up the set or the spark will arc through and that will continue to do so. I would really recommend checking the B+ voltage, you can also get arcing in the CRT and that can crack the neck. Great to see someone still working on the old sets :)
     
  11. #12

    Expert

    Nov 30, 2010
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    When I worked on vacuum tube TV's, they had regulation circuits for the anode voltage. Are you saying the designs have changed in the last 45 years? :eek:

    :D
     
  12. Hypatia's Protege

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    Mar 1, 2015
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    So... The arc is from the anode connector to the dag?
     
  13. #12

    Expert

    Nov 30, 2010
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    That's the way I read it, at least from someplace along the anode wire to the dag. Usta carry spares in my truck, but nowadays the wire is probably molded into the flyback potting so it isn't easily replaceable.:(
     
  14. Robert Schaaf

    New Member

    Jul 5, 2015
    3
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    That's funny! you sound like my dad! yes :) and when the HV is at 35 KV they will arc through the insulation of the flyback, the wire, all over. Some sets would shut down but others wouldn't and the protection circuits weren't always working right. It sounds like his set has a current detector that shuts it down after it arcs.
     
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  15. Hypatia's Protege

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    Mar 1, 2015
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    @mrel
    If the arc is indeed striking 'across the glass' from the anode connection to the aquadag -- just paint the 'areola' with 'high voltage dope', thoroughly clean the connector of any carbon traces and you should be good to go!:cool:

    Best regards
    HP
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    Once or twice I've fired up a repaired CTV before the RTV has cured - the electrostatic attraction causes thin filaments of silicone rubber to reach out for anything at a lower potential, there's usually a bit of faint crackle - but very rarely any actual cracking over.

    The Dow Corning product goes hard and brittle as it ages, I've found that some brands of RTV aren't as water repellent as the makers claim when I've used it on motorcycle HT leads.
     
  17. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Do see crack in the high voltage wire where the spark jump to the picture tube.
    mrel
     
  18. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    If the voltage had jump from 120 volt to 135 volts would this television put out more X-Ray?
    If the voltage gone higher as in your post if putting silicone on the wire can stop the spark jump to the picture tube if voltage go higher than 135 volt which is high would that put more X-ray out?
    mrel
     
  19. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    In that case the problem is indeed a faulty anode lead and, possibly, excessive EHT...

    If the failure is indeed owed to excessive EHT corollary to faulty LV regulation (or any etiology) you are advised to repair the electronic fault prior to repairing the anode lead! --- Don't worry about your X-ray exposure in this matter! Worst case dose under such circumstances will be insignificant -- that said, it is advisable to confirm that the EHT level does not exceed spec prior to returning the receiver to service...

    Best Regards
    HP
     
    Last edited: Jul 7, 2015
  20. mrel

    Thread Starter Active Member

    Jan 20, 2009
    97
    1
    Since i am not television repair person i just a hobbyist interested in electronics,I will patch the crack in high voltage wire where spark jump with silicone And after patching the wire and if a new area of the wire start spark that mean maybe got problem with high voltage.
    mrel
     
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