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Any parts of a LASERJET 5Si that can be salvaged?

Discussion in 'Electronic Repair' started by Ignoramus26555, Jun 23, 2005.

  1. Joseph Gwinn

    Joseph Gwinn Guest

    It goes the other way: To get through the holes, the frequency would
    need to be much higher than 2450 MHz.

    The rule of thumb is that the wavelength of the radiation in question
    must fit into a hole in the metal sheet. The higher the frequency, the
    shorter the wavelength. The relevant equation is that the product of
    frequency and wavelength equals the speed of light.

    So, for 2450 MHz: (2450*10^6)(wavelength)=3*10^8 meters/second, so
    wavelength= 0.122 meters, or 4.8 inches diameter. Actually, there will
    be significant energy leaking through if a half wavelength fits, so the
    issue really starts at about 2.4 inches. The cutoff function is
    complicated near one wavelength.

    Joe Gwinn
     
  2. Joseph Gwinn

    Joseph Gwinn Guest

    A CRT that's not connected to the HV lead won't have any path to ground to
    bleed the charge off, it'll pick up static from the air over time.[/QUOTE]

    The issue with CRTs is that the glass dielectric, having been kept at
    many tens of kilovolts for years, will store charge deep in the glass,
    and this charge cannot be eliminated quickly. The phenomena is called
    "dielectric adsorption" or "soakage". One can short such a CRT for a
    week, remove the short, and see the voltage magically spring back. So
    leave it shorted.

    Big capacitors can do this as well, especially the big oil-paper
    capacitors used in HV power supplies. These can store a lethal jolt.

    This same phenomena is used in Electret microphones, where a thin layer
    of teflon stores the HV charge needed to make the microphone work.

    Joe Gwinn
     
  3. What is the arc distance for dry air, 12kV per inch or something like
    that? I definitely wouldn't be trying it with 25kV. :)

    Tom
     
  4. For my wife's Diplomat microwave oven and my Nokia cellular telephone,
    the answer is yes. :)

    Tom
     
  5. They are probably well-insulated for their own particular frequency.

    Tom
     
  6. The issue with CRTs is that the glass dielectric, having been kept at
    many tens of kilovolts for years, will store charge deep in the glass,
    and this charge cannot be eliminated quickly. The phenomena is called
    "dielectric adsorption" or "soakage". One can short such a CRT for a
    week, remove the short, and see the voltage magically spring back. So
    leave it shorted.[/QUOTE]

    Dielectric absorption is one of the factors that the Sencore LC line
    of capacitor/inductor testers measures. Thanks.

    Tom
     
  7. TV discharge is easy. A stick with a nail in the end, that has a wire
    attached that is 'clipped' to the metal chassis. The nail is (when holding the
    wood stick - and insulated nicely (broom stick...) is slid under the HV plug.
    The arc will be under the plug cap and should be heard. e.g. if not - try again
    and wiggle around. Once done, or decided not needed - then the nail on stick
    is used (still attached - just in case) - and is hammered - slightly - through
    the metal seal that serves as the high voltage connector. Air flow will follow.
    Allow a slow flow. Breaking rapidly might implode the 'tube' end through the screen.
    So that is the reason to punch it with a nail. (or punch...)

    Naturally, it is a hasmat item - lead in the glass, phosphor in the screen, metals in
    the metals... Best to be left alone.

    Martin
     
  8. jakdedert

    jakdedert Guest

    I remember getting 'bitten' by an electric fence on which I played a stream
    of water from a garden hose, as a kid. The charger was the 'pulsed' type
    which used a 6v battery, inductor and 'balance beam' switcher for power.
    The hose had no nozzle on it, so I was using my finger to direct the spray.
    The distance was only a few feet, and the jolt was roughly comparable to
    touching the fence directly--it was never too effective even with direct
    contact...

    jak
     
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