Connect with us

Television discharge question

Discussion in 'Electronic Repair' started by Steve, Aug 25, 2004.

Scroll to continue with content
  1. Steve

    Steve Guest

    Hello,

    I have an old rear projection television that I would like to take
    apart and use the frame for another project. The television has not
    been plugged in since the year 2000. Do I still need to discharge
    capacitors even though it hasn't seen AC in 4 years? Could anyone
    tell me how long it would take on average for the caps to discharge
    by themselves?

    Thanks in advance.
     
  2. Tim Perry

    Tim Perry Guest

    YES

    Could anyone
    it dosent matter assume they are charged just as you should assume a gun is
    loaded when you handel it.
    never trust a bleeder resistor... it could be open
     
  3. Ross Herbert

    Ross Herbert Guest

    On Wed, 25 Aug 2004 02:05:03 -0400, "Tim Perry"

    |
    ||> Hello,
    |>
    |> I have an old rear projection television that I would like to take
    |> apart and use the frame for another project. The television has not
    |> been plugged in since the year 2000. Do I still need to discharge
    |> capacitors even though it hasn't seen AC in 4 years?
    |
    |YES

    And here I was thinking this was a troll......

    Tell me, how can any charge storage device (capacitor) or aquadag
    coating on a tube retain a charge when not having been powered up for
    4 years? Must be some magic new dielectric I haven't heard about, or
    the air is awfully dry.

    Personally, I wouldn't bother about charged capacitors causing
    problems after a week of not having been powered up, but I would still
    short the aquadag coating on the tube just to be sure. After 2 weeks I
    wouldn't even bother about that.


    |
    | Could anyone
    |> tell me how long it would take on average for the caps to discharge
    |> by themselves?
    |
    |it dosent matter assume they are charged just as you should assume a gun is
    |loaded when you handel it.
    |
    |>
    |> Thanks in advance.
    |>
    |
    |never trust a bleeder resistor... it could be open
    |
     
  4. Steve

    Steve Guest

    If you were referring to me as a troll, I really hope I didn't come
    across as that way. I was looking for serious advice.
     
  5. Art

    Art Guest

    Actually after that period of time you probably will not have any problem
    disassembling the set.<
    handled improperly. Use extreme care in disposing and handling of these
    particular items. BTW it may be necessary to have them properly disposed of
    because or environmental laws in effect there in Canada. You may need to
    contact your local DPW department and ask the about correct manner as to
    resolving that problem. <
    of the HV leads to the crts and have at it when trashing one of these. You
    can always have a service company come out and remove the guts from the unit
    but they will charge for a service call and labour to do so.<
    imported Fosters; Cheers Gov, hopefully you get this resolved.
     
  6. Asimov

    Asimov Guest

    "Ross Herbert" bravely wrote to "All" (25 Aug 04 12:12:46)
    --- on the heady topic of "Re: Television discharge question"

    RH> From: Ross Herbert <>

    RH> On Wed, 25 Aug 2004 02:05:03 -0400, "Tim Perry"

    RH> |
    RH> ||> Hello,
    |>
    |> I have an old rear projection television that I would like to take
    |> apart and use the frame for another project. The television has not
    |> been plugged in since the year 2000. Do I still need to discharge
    |> capacitors even though it hasn't seen AC in 4 years?
    RH> |
    RH> |YES

    RH> And here I was thinking this was a troll......

    RH> Tell me, how can any charge storage device (capacitor) or aquadag
    RH> coating on a tube retain a charge when not having been powered up for
    RH> 4 years? Must be some magic new dielectric I haven't heard about, or
    RH> the air is awfully dry.


    PURISTS!

    The "YES" reply is in practice wrong, maybe even a little ignorant?
    Realize, the crt glass has some leakage on the order of 10^14 ohms.
    Say we have an aquadag capacitance of 0.005uF, then the time constant
    is 500,000 seconds. Assuming 5 time constants for a nearly full
    discharge this is 2,500,000 seconds or about 1 month. Clearly after 4
    years there is practically no charge left.

    A+s+i+m+o+v

    .... High voltage can give a dangerously uncomfortable discharge.
     
  7. Ross Herbert

    Ross Herbert Guest

    On Wednesday, 25 Aug 2004 23:17:46 -500, "Asimov"

    |"Ross Herbert" bravely wrote to "All" (25 Aug 04 12:12:46)
    | --- on the heady topic of "Re: Television discharge question"
    |
    | RH> From: Ross Herbert <>
    |
    | RH> On Wed, 25 Aug 2004 02:05:03 -0400, "Tim Perry"
    |
    | RH> |
    | RH> || |> Hello,
    | |>
    | |> I have an old rear projection television that I would like to take
    | |> apart and use the frame for another project. The television has not
    | |> been plugged in since the year 2000. Do I still need to discharge
    | |> capacitors even though it hasn't seen AC in 4 years?
    | RH> |
    | RH> |YES
    |
    | RH> And here I was thinking this was a troll......
    |
    | RH> Tell me, how can any charge storage device (capacitor) or aquadag
    | RH> coating on a tube retain a charge when not having been powered up for
    | RH> 4 years? Must be some magic new dielectric I haven't heard about, or
    | RH> the air is awfully dry.
    |
    |
    |PURISTS!
    |
    |The "YES" reply is in practice wrong, maybe even a little ignorant?
    |Realize, the crt glass has some leakage on the order of 10^14 ohms.
    |Say we have an aquadag capacitance of 0.005uF, then the time constant
    |is 500,000 seconds. Assuming 5 time constants for a nearly full
    |discharge this is 2,500,000 seconds or about 1 month. Clearly after 4
    |years there is practically no charge left.

    The actual time will depend on;

    a) moisture content of the atmosphere
    b) conductivity to chassis

    In practical situations it won't take anywhere near this estimated
    maximum to self discharge to a safe level.
     
  8. Asimov

    Asimov Guest

    "Ross Herbert" bravely wrote to "All" (26 Aug 04 04:31:20)
    --- on the heady topic of "Re: Television discharge question"

    RH> From: Ross Herbert <>

    RH> |Realize, the crt glass has some leakage on the order of 10^14 ohms.
    RH> |discharge this is 2,500,000 seconds or about 1 month. Clearly after 4
    RH> |years there is practically no charge left.

    RH> The actual time will depend on;

    RH> a) moisture content of the atmosphere
    RH> b) conductivity to chassis

    RH> In practical situations it won't take anywhere near this estimated
    RH> maximum to self discharge to a safe level.


    Yes, even dry air is about 100 times more conductive than glass but
    this neglects that the circuit wiring and anode boot insulate the air
    path. The remaining path, assuming the focus divider is open circuit,
    is via the HV rectifier but its leakage is of the same order as glass.
    So then that could double the speed of the discharge. Okay, 2 weeks?!

    A+s+i+m+o+v

    .... I know flyback, ultor, and 47 other dangerous words.
     
  9. Tim Perry

    Tim Perry Guest

    Gentelman, question was not "theoretecly how long will a HV cap hold a
    charge" it was "Do I still need to discharge
    as: "i don't know what i am doing so how do i do this safely?"

    when working with old HV electronics never assume. tie a conductor to the
    chassies and use it to touch everything.

    dont even assume that it hasen't been plugged in in 4 years.

    im recomending you follow basic safety procedures.

    we can guess that 'probably' every thing is discharged and 'maybe' the
    safety bleeders are intact.... but do you want to find out the hard way that
    someone guessed wrong?
     
  10. Ross Herbert

    Ross Herbert Guest

    On Thu, 26 Aug 2004 21:37:40 -0400, "Tim Perry"

    |Gentelman, question was not "theoretecly how long will a HV cap hold a
    |charge" it was "Do I still need to discharge
    |> capacitors even though it hasn't seen AC in 4 years?" which i interpreted
    |as: "i don't know what i am doing so how do i do this safely?"
    |
    |when working with old HV electronics never assume. tie a conductor to the
    |chassies and use it to touch everything.
    |
    |dont even assume that it hasen't been plugged in in 4 years.
    |
    |im recomending you follow basic safety procedures.
    |
    |we can guess that 'probably' every thing is discharged and 'maybe' the
    |safety bleeders are intact.... but do you want to find out the hard way that
    |someone guessed wrong?
    |

    All good advice for those cases where you don't know for a fact how
    long since a TV has not been powered up. In the Op's case he KNOWS for
    a fact that the TV hasn't seen power for 4 years.
     
  11. Steve

    Steve Guest

    You are correct. I've never discharged a television before and was
    wondering how to do it safely. I've had the television since it was
    bought new and know for a fact the last time it was plugged in was
    in early 2000. Thank you all for your input, I will be calling a
    service company to dismantle it and dispose of the guts.
     
  12. Barry S.

    Barry S. Guest

    Like a screwdriver w/clip lead to chassis? Or a test light? Any
    recommendations for "discharge devices?"


    __________________
    Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
    N37.3 W122.0
     
  13. RonKZ650

    RonKZ650 Guest

    I don't know the original question, but pretty much sitting overnight will
    discharge the HV or filter caps. Sitting longer than a couple days=no charge
    left.
     
  14. James Sweet

    James Sweet Guest

    Usually a few minutes is enough to discharge it, however that's no reason
    not to manually discharge it no matter how long it's been sitting. It may
    have been off for 10 years, but like a gun, always treat it as if it's
    loaded.
     
  15. Peter Kolbe

    Peter Kolbe Guest

    Lets hope nobody decided to plug the set in without you knowing!
     
  16. RonKZ650

    RonKZ650 Guest

    To be perfectly honest, sitting overnight is ample time to discharge 99.999% of
    caps or CRTs. I'd say 4 years you're relatively safe.
    Ron
     
  17. Jerry G.

    Jerry G. Guest

    Did you ever try to remove the anode cap from a CRT on a set that has been
    sitting for a week, and you didn't discharge it? There are some models that
    are designed to slowly discharge on their own, but not all of them. If not,
    try it, and let me know how you feel after!

    After several months, I have been zapped from anode caps. This is because
    the source DC resistance is extremely high in some of these sets.

    As for the power supply, after about 2 to 3 days, I would say it will be
    safe, because there are other components connected to the caps, and they
    have resistive characteristics. Some of the manufactures have a bleeder
    resistor built in for the main filter caps. But, I would not trust this
    without first checking this out.

    In theory, a good cap can hold the charge for a long time. I have charged up
    caps to several hundred volts, and the next day when I checked them with my
    DVM, there was still too much for comfort.

    Considering the natural leakage in the caps of any device, after about a
    week or so, they should normally be discharged. When I work on anything that
    uses voltages in excess of about 50 Volts, I check with a DVM first before
    my hands go in to it. If I have to, I find a way to discharge the voltage
    that is present, or I work in a fashion where I don't have to be directly
    handling the components at their leads.

    Normally when I work on these sets, I check to see if the caps are charged.
    If so, I have a 20 Watt 220 ohm resistor with a set of leads that I put
    across the main caps for a few seconds to discharge them. I am concerned
    about the main electrolytic caps that are holding at least a few hundred
    volts.

    In many of the switching supplies, depending on the design, they self
    discharge across the other resistive components anyways. I found that after
    about a few minutes or so, they are very safe to handle.

    The best way to work is with caution.



    --

    Jerry G.
    ======


    To be perfectly honest, sitting overnight is ample time to discharge 99.999%
    of
    caps or CRTs. I'd say 4 years you're relatively safe.
    Ron
     
  18. RonKZ650

    RonKZ650 Guest

    Did you ever try to remove the anode cap from a CRT on a set that has been
    Interesting, I can say I've been in the business for 27 yrs and have never once
    been shocked off a tube that has sat overnight, regardless of whether it has a
    bleeder resistor in the design or not. I've been mighty lucky all these years I
    guess :)
     
  19. D MARSHALL

    D MARSHALL Guest

    i fined it safer to dispose of old tubes
    is to snip of the nipple on the end of the
    tubes neck under the crt board, there wil be a plastic
    keyway over the pins on tube remove it
    gently or cutt into the plastic end between the
    pins.
    where protection goggles and wrap some
    rags around the neck on the tube before you
    do this.
    after that you move it around without
    it inploding.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-