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Taking Apart A Television (is this safe)?

Discussion in 'Electronic Repair' started by [email protected], Jan 30, 2005.

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  1. Guest


    Im planning to take apart an old cathode ray tube television I have.
    Television is an amazing device, invented by the great Philo Farnsworth
    when he was only twenty one years of age. Should I be careful for
    anything specific? Would the selenium be a problem? Chemicals?
    Thank You
  2. Marko

    Marko Guest

    The CRT is the primary concern for two reasons: It can implode
    sending chards of glass everywhere and it acts as a huge high-voltage

    Do you plan to take the TV apart and reassemble/reuse it? If not, you
    might want to vent the CRT to eliminate the possibility of implosion.
    This can be done by breaking the glass nipple off the neck.

    Regarding the HV, even if the TV is broken and/or hasn't been used in
    years, there can be enough residual HV on the CRT to knock you on your
    butt. There is probably not enough to kill you but it's surprising
    what injuries can be sustained when you jerk your hand back after
    being zapped with 20KV.

    Most people use a long screwdriver to discharge the CRT. You'll
    probably note a fat red wire going from the flyback transformer to the
    bell (2nd anode) of the CRT. While holding the screwdriver shaft in
    contact with the metal chassis, work the tip under the rubber cap of
    the 2nd anode connector on the CRT. If there is a charge, you'll hear
    a "snap" as it is discharged through the screwdriver to the chassis
    ground. You won't feel any shock because you are being careful to
    keep that screwdriver in contact with the chassis the whole time.
    (Guess what happens if your screwdriver isn't contacting the chassis?)

    One note here... even after the CRT is discharged, it can and will
    build up a new residual charge - even if the TV is not turned on or
    even plugged in. So, discharge it again if you plan to put your hand
    anywhere near that 2nd anode connection on the CRT. The charge is in
    the CRT, not the red wire.

    Also, don't have any expensive electronics near the set when you
    discharge the CRT. There is a little EMP that is generated that can
    damage some devices. I've lost a few PC keyboards this way.

    As far as chemicals, I think you're OK. There may be cadmium in the
    phosphor but you're not going to mess with that. There is lead in the
    solder - try not to breath it and don't eat it. Wash your hands
    before eating. You mention selenium... does this set have an old
    selenium rectifier? It's probably not dangerious as long as you don't
    eat it. (I guess you can eat a little - RDA of selenium is 55
    micrograms according to the national Academy of Sciences - seriously.)

    Good luck.
  3. Eric

    Eric Guest

    Television invented by Philo Farnsworth?
    Are you re-writing history?


    Im planning to take apart an old cathode ray tube television I have.
    Television is an amazing device, invented by the great Philo Farnsworth
    when he was only twenty one years of age. Should I be careful for
    anything specific? Would the selenium be a problem? Chemicals?
    Thank You
  4. CJT

    CJT Guest

    I think the other poster hit most of the high points. I would add that
    there can be sharp edges on the sheet metal, pointy wire ends, etc. on
    which you can cut yourself. And some of those old chassis are quite
    heavy. Tubes other than the CRT break, too, and some contain mercury
    and/or other nasties in addition to the obvious danger of broken glass.

    I think the selenium rectifiers are a hazard primarily when they fail
    and emit gases.

    If the set has been powered up recently, other capacitors besides the
    CRT can hold a charge.

    Occasionally you'll see a part that is spring loaded.

    And you never know what else you might find in an old TV. The cat may
    have visited, or somebody could have hidden a stash.
  5. Most people use a long screwdriver to discharge the CRT. You'll
    You are supposed to arc the anode lead to the DAG, not the chassis ground.

    One way is to use a wire with alligator clips, one on the screwdriver and
    another on the metal DAG braid usually wrapped around the back of the picture
    tube, and then gently insert the tip of the driver under the anode cap towards
    the connection point. You'll know when you've discharged it (if it was
    charged) when you hear a POP.

    It is recommended that you use a high value resistor in the ground path,
    though. - Reinhart
  6. James Sweet

    James Sweet Guest

    The DAG is connected right to the chassis ground in every set I've seen, so
    shorting to the metal frame if there is one is generally fine. Most TV's
    don't have much of a metal frame though so it's easier to clip the wire to
    the spring strap around the bell of the tube that contacts the dag.
  7. James Sweet

    James Sweet Guest

    How old is this TV? If it's old enough to contain tubes other than the CRT
    or a selenium rectifier it might be worth something as a collectible.
  8. Guest

    Wow...Thanks guys. I didnt realize that I would have to take such
    precautionary measures. The television is a 1999 sony, I believe. It
    was struck by lightning and now the image is so tinted that the TV is
    not worth salvaging. I just wanted to take it apart, examine the
    components and learn. And yes, many people did indeed contribute to the
    great invention that is television;

    Vladimir Zworykin
    Paul Nipkow
    G.R Carey
    Jons Berzelius
    Philo Farnsworth

    We owe a great debt of gratitude to those men.
  9. Laughing. Seleniums went out of the picture long before tubes.
  10. Guest

    I have been working on color TVs since 1955 when I was doing some
    college work on color prototype sets, even before the RCA CTC-1 came
    out. To the best of my knowledge, no color set has ever been
    manufactured in the USA using selenium rectifiers. The current levels
    were too high and the selenium rectifiers got so hot that they were
    relegated to mostly B+W sets and to automobile battery chargers where
    they tended to be used with ventilation. The very early RCA - CTC-1
    vintage sets used multiple 5U4s.

    One early CBS prototype set, non-rotating wheel, built right after the
    RCA NTSC format was approved, was a 2-cabinet affair. One cabinet was
    just for the power supplies, the other cabinet used a round 16" metal
    picture tube with a 12" flat color screen mounted inside the metal
    tube. It took days to get the set purity and convergence set up, and
    you didn't dare move the set once it was set up because the set was so
    sensitive. This was at the University of Florida - Gainesville. I
    graduated in 1957, and don't know what happened to that old CBS set.
    It generated enough heat that we couldn't run it more than a couple of
    hours except in the winter. No air-conditioning in the labs back in
    those ancient days.

    H. R. (Bob) Hofmann
  11. Guest

    wrote:(snip)yes, many people did indeed
    contribute to the
    If I recall correctly, Zworykin was responsible for the cathode ray
    tube, which Baird later attempted to use in experiments with the first
    TV signal transmission systems.

    But don't quote me on that! ;-)
  12. James Sweet

    James Sweet Guest

    Try degaussing the tube, that might fix it right up. Sony makes a good set
    and that's a fairly new one.
  13. Jerry G.

    Jerry G. Guest

    I just read all of these comments.

    The only very dangerous thing you should be worried about, is if you
    accidently break the CRT. Other things to worry about is if there is any
    high voltage retained in the CRT anode, and if there are any dangrous
    voltages stored in the main capacitors.

    It is difficult over an email to describe procedures such as these, in a way
    that would be reliably safe for someone else of no experience to follow.
    Getting in to a TV set without the proper training and supervision is
    something that is not considered safe by any means. In service centers, they
    don't even like their experienced technicians to work on sets when alone, in
    case of an accident.

    If you want to learn something worth while about TV, take a structured
    electronics coarse, and then after you do a few years of studying, you may
    have enough basics to read some books to get an idea of what goes on in a TV

    Taking one apart will not really teach you more than how to take it apart,
    and maybe if you are lucky, you will learn about what a mild jolt can do to

    Find out from your local city hall about where to take the set for disposal.
    This is the safest for you, your family, and the environment.



    Romeo E. Albert
  14. James Sweet

    James Sweet Guest

    Really the best way to learn is by learning to fix them rather than just
    take them apart. Contrary to what some say, TV's are not terribly dangerous
    to work on, I'm completely self taught as I'm sure many of the professional
    techs here are. If I hadn't taken apart TV's to work on them I'd have never
    learned how in the first place. That said, read up on the safety first,
    there's no need to freak out and go overboard but it is important to know a
    few basic rules and have common sense when working on these things. Read the faq first, then familiarize yourself with using your
    DMM, practice some soldering and desoldering, go out and find some broken
    TV's, then browse through the TV section of the FAQ again and dig in. Post
    here if you get stuck and keep at it, sooner or later you'll get the hang of
  15. CJT

    CJT Guest

    I seriously doubt a 1999 television will contain a selenium rectifier.
  16. CJT

    CJT Guest

    I'm not sure how to parse that sentence. Seleniums disappeared before
    tubes disappeared, but there were certainly sets containing both.
  17. James Sweet

    James Sweet Guest

    It won't, or tubes, but that discussion was before we knew the age of the
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