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questions anode crt

Discussion in 'General Electronics Discussion' started by gamer87, Apr 9, 2019.

  1. gamer87

    gamer87

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    Mar 11, 2017
    What is the correct procedure for removing the anode cap from the CRT without tearing?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  3. gamer87

    gamer87

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    Mar 11, 2017
    To discharge the tube I used a screwdriver under the anode cap and scratched the tube, is it bad and permanently damaged?
     
  4. Cannonball

    Cannonball

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    May 6, 2017
    I would use a jumper wire with alligator clips on each end. clip one end to a ground ( the chassis ) and the other end clipped to a screwdriver with an insolated handle. Slide the screwdriver under the cap to the metal clip to discharge the picture tube.
     
  5. gamer87

    gamer87

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    Mar 11, 2017
    the friction of the screwdriver with the crt scratch it, is that bad? It is very difficult without scratching the pipe because the
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    You should not be messing with the anode cap unless you have experience with this. The CRT acts as a large capacitor that can retain a high voltage for several days unless it is discharged. The anode cap is often difficult to remove after being in place for years, exposed to ozone and other atmospheric contamination while the volatile organic compounds (VOCs) of it original composition slowly evaporate or break down into other chemistry...

    The safest way to discharge the anode of a CRT is to use a length of high-voltage, stranded, high-voltage ignition wire to "short out" the CRT anode BEFORE attempting to remove the anode cap. Be sure the "strands" are actually wire and not carbon-coated plastic!

    Use a flat plastic insulated stick, such as a disposable "fast food" plastic knife, to carefully lift one side of the rubber flap on the anode cap, thereby exposing one of two metal wire clips that secure the anode cap to the CRT anode electrode. Strip off about two inches (50mm) of insulation from the high-voltage ignition wire and fan out the strands until only two or three are protruding from the end of the wire. You will use these strands to "short out" the anode terminal of the CRT BEFORE removing the anode cap. Fold and wrap the remaining strands around these few strands and then twist these two or three strands tightly together.

    Now strip the other end of the ignition wire and connect it to the outside coating of the CRT as shown in the website that @Harald Kapp linked you to. DO NOT rely on the chassis for this "ground" connection! Finally, slip the plastic stick under the anode cap far enough to reach the two metal clips securing the anode cap to the CRT. Slide the bare end strands of the ignition wire under the plastic stick until the wires contact one of the metal clips. Leave in place a few minutes and then use your fingers to gently squeeze the two metal clips under the rubber cap, allowing the cap to be separated from the anode terminal. If the rubber cap has "welded" itself to the CRT envelope, use the plastic rod to carefully separate the rubber cap from the CRT glass.

    If you are going to make a career servicing CRTs in this manner, you can make a more permanent connection between the strands of the ignition wire and the plastic stick by using a thin layer of Super Glue to attach the wires to the stick, folding the ends back around the end of the stick to ensure better contact with the anode cap. Make sure you don't accidentally insulate the wire with the Super Glue. You could even get fancy by adding an alligator clip to the opposite end of the shorting wire. Maybe add a big red tag explaining what this spiffy "tool" is used for.

    The cathode ray tube (CRT) is under very high vacuum on the inside, essentially zero pounds per square inch. The outside is at atmospheric pressure, approximately 14.7 pounds per square inch. Any scratches on the outside surface of the CRT present a potential point of future failure if the CRT is even slightly bumped while handling the heavy glass envelope. You do not want to be anywhere near the CRT if it should implode, because sharp glass shards will go flying everywhere.

    There is a safe way to de-commission a bad CRT that involves first placing it completely inside a sturdy cardboard or wooden box. A heavy metal stake is then driven into the center of the face of the CRT. Most of the glass will shatter and be safely contained by the box, which can then be re-cycled or otherwise disposed in a landfill. This is often accompanied by a very satisfying whooomp! sound as air rushes in to replace the former vacuum inside the CRT.:D
     
    Cannonball and Harald Kapp like this.
  7. gamer87

    gamer87

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    Mar 11, 2017
    I crt using screwdriver on the crt ground and below the anode cap but the friction of it with the crt caused some scratches, that crt is going to die because of these scratches? if scratching can recover?
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    Everything dies... eventually. Just be aware that scratching the glass envelope of a CRT does nothing to prolong the process, and it may tend to speed things up if the CRT is handled carelessly. And, no, you cannot recover from scratching.

    I owned a large color TV in the 1960s that developed a very visible but tiny crack. but still produced an excellent color picture, back in the day... This type of TV was considered fine furniture back then, at least by the people who sold it to me for a goodly sum of money, but there was no warranty for "cosmetic" damages. I was afraid that the CRT was going to implode one day with one of my four young children sitting closely in front of it. There was a clear, transparent, barrier window between the CRT faceplate and the rest of the viewing area, but that crack nevertheless worried me.

    Eventually the TV died and we got rid of it with no further ado. It probably wound up in a landfill somewhere, CRT still intact, still installed, still waiting to implode. So, if you handle your CRT gently, it may be okay to place it back in service. I didn't want to alarm you, but I did want you to be aware of the risks. Glass breaks. And glass under vacuum breaks violently.

    We had a large glass Bell Jar vacuum chamber in one of the laboratories where I worked. It was surrounded by a heavy-gauge aluminum shield with perforations cut out to allow viewing. The glass jar was supported on one side by hose clamps that encircled the jar and was attached to a motorized host mechanism that lifted the jar to allow experiments to be set up inside of it. One day I came to work to discover that somehow the jar had shattered overnight, presumably while under vacuum, since that was the usual way to leave a vacuum system to prevent the internal absorption of water vapor. It took most of the day to clean up the glass and several more days before a new Bell Jar could be ordered, received, and carefully installed.

    We never did discover why or how the thing managed to break, although it was quite common for them to develop cracks. If the cracks leaked air into the vacuum, we just painted over them with a sticky substance that hardened to a leak-proof seal... well, more or less. This was not the usual ultra-high vacuum system since it relied on elastomer seals between the base and the glass Bell Jar. But all we needed was a "gud enuf" vacuum to prevent burning out tungsten heater wires. Our really high-vacuum systems used copper-metal knife-edge seals that could be baked (heated) to drive off water vapor. We also avoided aluminum because it really holds on tightly to water molecules compared to stainless steel. We also needed gloves to avoid depositing body fluids inside the vacuum chambers. Oh, well... it was fun while it lasted.
     
  9. gamer87

    gamer87

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    Mar 11, 2017
    flannel and isopropyl alcohol is good for total crt cleansing?
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    I use Viva soft paper towels instead of flannel, and 91% isopropyl alcohol, to clean almost everything electronic. You should make sure the alcohol doesn't dissolve the conductive AcquDAG coating that is sometimes applied to the exterior of the CRT envelope.
     
  11. gamer87

    gamer87

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    Mar 11, 2017
    If the isopropyl alcohol dissolves the conductive coating so I will not use it, if it dries plastic then I will not use it

    Aquadag is a compound applied internally in the crt or externally in the crt? externally with the application of isopropyl alcohol may
     
    Last edited: Apr 10, 2019
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