Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dissecting a cathode ray tube television

  1. Apr 20, 2008 #1
    I'm considering dissecting an old, color cathode ray tube television. Do cathode ray tube televisions have capicitors in them that could shock me?
     
  2. jcsd
  3. Apr 20, 2008 #2

    turbo

    User Avatar
    Gold Member

    Please do not play around with electronics if you don't know what you're doing. I'm not going to give you any information regarding TVs because that is not a safe place for an amateur to start.
     
  4. Apr 21, 2008 #3
    Not to mention the large evacuated glass thingie the picture appears on... a very dangerous thing even when the tv is switched off & disconnected from the mains.
     
  5. Apr 21, 2008 #4
    Why would the glass screen of a tv be dangerous even when the tv is switch off and disconnected? Do you think it would be dangerous because it could break and cut someone?
     
  6. Apr 21, 2008 #5
    What is a safe place for an amateur to start?
     
  7. Apr 21, 2008 #6

    turbo

    User Avatar
    Gold Member

    Start with battery-powered circuits that you can bread-board. Radio Shack has bread-board kits with components that you can learn from. Learn the functions of the components, how to read the values of those components from markings, how to measure the values using a digital multimeter, etc, etc. Before you delve into AC or high-voltage DC circuits, you MUST learn how to test and safely discharge capacitors. They can kill you.
     
  8. Apr 21, 2008 #7
    Turbo,

    What does bread board mean?
     
  9. Apr 21, 2008 #8

    turbo

    User Avatar
    Gold Member

    A bread-board is a perforated plastic circuit board on which you can build circuits using discrete components.
     
  10. Apr 21, 2008 #9
    There is a vacuum inside the tube, so it could implode and send glass shards flying everywhere. Also there may be toxic chemicals.
     
  11. Apr 21, 2008 #10
    In the tv show MacGyver, MacGyver once made a bomb out of the cathode ray tube of a tv, and that's what sparked my interest.
     
  12. Apr 24, 2008 #11
    The capacitors in a crt are large enough to kill you and they can keep a charge for years after being plugged in.
     
  13. Apr 24, 2008 #12

    berkeman

    User Avatar

    Staff: Mentor

    Well there's a healthy interest in learning.... :rolleyes:

    As others have said, please learn a LOT more before messing around with a TV or computer monitor. In addition to the large mechanical energy stored in the evacuated CRT itself, the high voltage circuit that charges up the CRT (the conductive coating on the faceplate is held at around +25kV with respect to the electron gun in the back/neck of the CRT), can hold a residual voltage of several kV when turned off. And that residual charge sticks around for an amazingly long time in some cases. Certainly several days (probably not years though).

    There are also AC mains capacitors like after the input bridge rectifier, which can stay charged up to hundreds of volts for days as they leak down. Very unpleasant when brushing up against exposed leads (Quiz Question -- why do I know that? Ouch.).

    Finally, there is no safe "ground" in television sets. They often use a "hot chassis" design, which means that if you do not use an isolation transformer in working with open TVs, you will either blow up your oscilloscope or electrocute yourself. Or both (now THAT would be a bad day, to have both happen....).

    So a) start with more basic circuits to learn from, and b) don't make your learning aimed mostly at how to blow stuff up.
     
  14. Apr 24, 2008 #13
    Because they still retain a charge, and pack quite a punch even when unplugged, don't do it.
     
  15. Apr 24, 2008 #14
    There is alot of chemicals inside a CRT, such as lead and phosphorous in form of a fine powder which if disturbed will disperse into the air.
     
    Last edited by a moderator: Apr 24, 2008
  16. Jun 14, 2008 #15
    You could get some damage playing with something like that, but you can also discharge capacitors with a resistor (~50-200k Ohmms value should be fine) connected to two wires.
     
  17. Jun 14, 2008 #16

    NoTime

    User Avatar
    Science Advisor
    Homework Helper

    Most new CRT circuits and power supplies have built in bleeder circuits which discharge the voltage fairly quickly.
    As long as the bleeder circuits themselves are not broken which happens from time to time.

    Older CRT implementations could hold a significant charge for months.
     
  18. Oct 28, 2008 #17
    DON'T DO IT! EXTREMELY DANGEROUS!

    I have seen dangerous charges on CRT's that have been disconnected for a couple years.

    Just don't do it.
     
  19. Jul 28, 2009 #18
    Heck, yeah they do! Experienced repairmen usually won't even touch one until it's been sitting unplugged for a week or more. There can definitely be enough charge in TV capacitors to kill you.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Dissecting a cathode ray tube television
  1. 3d television (Replies: 22)

Loading...