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Soldering a Broken TV

Discussion in 'Electronic Repair' started by [email protected], Oct 29, 2006.

  1. Guest

    I started having trouble with my TV after it was moved in a U-Haul from
    San Francisco to Seattle. I managed to locate a faulty solder joint on
    the board. Applying pressure to the joint with a strip of wood fixes
    the problem.

    My problem is this: I am very experienced with electronics and
    soldering, but I have little experience when it comes to high voltage.
    I need to fix the solder joint but I have no hardware to properly
    discharge any high voltage capacitors in the TV. I don't think this is
    a problem as the faulty solder joint is attached to what appears to be
    a FET. However, it could also be a triac, which could mean that it's
    attached to a HV part of the circuit. I don't want to stick my head in
    there to find out exactly what it is. Would you advise fixing the
    solder joint without first discharging the TV?

    Thanks in advance!
     
  2. Huh?

    You're "very experienced in electronics and soldering" yet you don't
    know whether something is an FET or a triac?

    Michael
     
  3. Fix it that way. You don't have the skill set to do more.
     
  4. Just lay some steel wool or tinsel around where you will be working and
    it will short out any voltage.

    --

    You are living somebody else's dream. The whole world, laws
    and way of life; not your dream.


    Clyde Crashcup
     
  5. Guest

    I don't want to stick my head in between the high-voltage electronics
    and the CRT to see it more closely.
     
  6. Ken G.

    Ken G. Guest

    You dont need to discharge anything to do some soldering . The charge is
    held up under that big suction cup on the picture tube . Simply turn the
    set off and wait a few minutes for the filter capacitors to discharge by
    themselves , turn the board over then solder .
    In some cases when you walk up to a tv and touch metal parts you may get
    a static zap just like you do from the car door or door knob in your
    house .
     
  7. CJT

    CJT Guest

    That "big suction cup" has a wire extending from it to the HV section.
    Touching any bare section of that wire (although there shouldn't be
    any), or of the parts in the HV section to which it's attached, can
    give you a big surprise.

    The picture tube itself holds the charge.
     
  8. CJT

    CJT Guest

    That sounds like a recipe for problems later, when bits of steel wool
    left behind cause further shorts. Besides, putting steel wool on a
    board containing capacitors that aren't fully discharged already can
    discharge them through inappropriate paths.
     
  9. Responses like this are not constructive and downright dangerous.

    Simply leave the TV off overnight. That should discharge any capacitors
    that would affect soldering on the mainboard. The only possible remaining
    charge may be on the CRT anode but that only goes to the flyback and you
    should not need to disconnect it. And, that will almost certainly be
    discharged by then in any case.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  10. In nearly all CRT TVs and monitors less tha 30 years old, it goes directly
    into the flyback and bare sections would be extermely unlikely.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  11. Unless the ground to the outside of the kine is disconnected. Not a good
    thing to touch if you are standing on the ledge of a second floor window.
     
  12. James Sweet

    James Sweet Guest


    Just get in there and solder it, if the set has been unplugged for a few
    days there's no risk.
     
  13. I'm not sure I'd want to test it out this way, but in principle, if the
    ground only were disconnected after the set was turned off, there would
    be no voltage between it and ground.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  14. True, but when it is run that way and you just turned it off to twist the
    yoke . . . . .
     
  15. Guest

    I think a lot of the reponses so far have been attempts at humour.
    Possibly because you say youre very experienced yet dont know how to
    discharge a psu cap or the tube eht. No, you cant rely on them to self
    discharge over a day or so. Since youre experienced, figure it out.


    NT
     
  16. He made his skill level clear and the best advice for him is to not try.
    Fix it that way. You don't have the skill set to do more.
     
  17. HeHeHe... If it's run with the CRT ground disconnected, that's a different
    story. :)

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  18. bz

    bz Guest

    wrote in
    Go to the library. Get an older copy of the Radio Amateur's Handbook. It
    should show you how to make a tool consisting of a wire, a wooden dowel, and
    a resistor, that can be used to safely discharge high voltage capacitors.

    These devices were called 'crowbars' because that is what they essentially
    were, a crowbar with a heavy wire that connected it to ground.

    The operator would turn off the power, hang the crowbar on the high voltage
    line, grounding it, and work on the equipment, secure and safe. IF someone
    accidently turned on the power without removing the crowbar, it would blow
    fuses.

    Nowdays, a circuit that shorts the output of a power supply to ground in case
    of overvoltage output of the supply is called a 'crowbar' circuit, for
    reasons that should now be clear.





    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     

  19. You are describing a "Shorting Stick" which is a safe way to discharge
    a HV power supply to service the equipment. It was also used in
    broadcast transmitters, in case the safety interlocks failed. A crowbar
    is not current limited, it is a fail safe shutdown circuit, and you can
    expect damage if it is triggered.



    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  20. Guest

    discharging CRT skill easily learnt

    NT
     
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