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CRT HV wire repair ?

Discussion in 'Electronic Repair' started by robb, Jan 18, 2008.

  1. robb

    robb Guest

    I have a bad and good CRT. I want to swap out BAD CRT with the
    (known compatible) good one.

    The CRT's HV wires have a special plug/jack into the HV
    multiplier (flyback) so there is no flaky splicing to worry with.

    The good CRT has (too) short HV wire. The wire does not reach the
    HV multiplier (flyback).

    I was told that i can carefully cut under silicon blob where HV
    wire attaches to CRT and unsolder wire then solder the long one
    in place ?yes/no? Then re-cover with silicon.
    Let silcon dry/cure (**** completely ****) !!!

    Questions :
    0. Is this a feasible repair ?
    1. What silicon do i buy (from local hardware?) ? is that special
    silicon ?
    2. Good CRT has 2" copper tape over the silicon blob / HV wire.
    a. Do i need to replace this tape ?
    b. can i use aluminum tape like for duct work ? :)
    that is the real Aluminum tape with just sticky stuff
    (no foam /vinyl/etc)
    c. How can i get old piece copper tape to stick back ?
    d. Any alternatives to the copper tape ?
    3. Any special cleaning or surface prep needed to do this repair?

    thanks for any help,
    robb
     
  2. James Sweet

    James Sweet Guest

    What kind of CRT is this that the wire is soldered on? I've never seen on
    that didn't have a metal cup that the wire just clips into, not saying they
    don't exist, but I've yet to ever come across one.

    The copper tape is used as shielding, you can buy it from a lot of different
    places, just do a google search. You ought to be able to stick it back on
    with double sided plastic tape if the original adhesive is not reusable.
     
  3. robb

    robb Guest

    out of a Tek o-scope

    robb
     
  4. Arfa Daily

    Arfa Daily Guest

    Personally, I think that at last initially, I would feel inclined to leave
    the factory connection to the good CRT alone, and go down the splicing
    route. If you do a really nice job of soldering the two wire tails side by
    side with a generous 'blob' of solder to make sure that there are no spikes,
    you shouldn't have an intitial problem with corona discharge. When you are
    happy with the solder joint, use a piece of insulation sleeve, slit
    lengthwise, to cover the join. Before making the soldered joint, slide a
    couple of lengths of hetshrink tubing over the lead. When you have your slit
    tubing in place over the joint, work a bit of silicon rubber into the slit,
    around the joint, then shrink the first piece of tubing over the whole
    joint. When that has cooled down, slide the second (slightly longer) piece
    over the whole lot.

    I have spliced several high voltage wires of various types over the years,
    using basically this method, and have never had a problem. And at least if
    it doesn't work for you, you've then still got the damage-riskier option of
    trying to get a good bond at the actual CRT connection.

    Arfa
     
  5. Meat Plow

    Meat Plow Guest

    The OP wants to be careful with splicing in a scope. I reckon that any
    point in the HV lead that is not contiguous might have the possibility of
    generating some RFI which could have consequences when measuring delicate
    signals. I'll assume this is also the reason the anode cap is taped over
    with copper.
     
  6. Jim Yanik

    Jim Yanik Guest

    ever since TEK began making their own CRTs with the ceramic bell,they have
    affixed the anode lead to the CRT bell.
    I've seen maybe one failure of that joint in my 21.5 years
    there.Usually,it's because some customer tried to measure the anode V by
    digging under the silicone rubber seal.


    While at TEK,I had to splice a few 634 monitor anode leads,and we used a
    silicone rubber tubing to go over the soldered splice,then heatshrink over
    that to keep it in place. 10KV or more has a way of finding any pinhole or
    leakage path and making arcs,carbonizing a better path,etc.

    But I missed the reason WHY the OP wants to splice the CRT anode lead.
     
  7. robb

    robb Guest

    Hello Jim,

    OP here. The reason ....
    I want to replace a BAD CRT with compatible GOOD one.
    The GOOD CRT has an HV lead that is too short.

    The HV Anode Plug will not reach the socket on the HV multiplier
    that is sitting inside the PS. It is about 1.5 '' to short with
    HV lead pulled taught.

    I read that one can cut the CRT anode silicon cover , unsolder
    the long lead and then solder long lead to GOOD CRT and then
    recover with silicon.

    I am asking ...
    1. is this possible or feasible ?
    2. What silicon do i use (from local hardware store) ? "RTV" is
    not there just %100 silicon sealer
    3. is there any special surface prep to perform ?
    4. What can i do to replace or re-glue the 2" copper tape that
    was covering the silcon anode mount point ?

    and any other ideas i did not list,
    robb
     
  8. Well for the foil tape you might be able to use aluminum foil tape which is
    for air duct work. They sell it at most hardware stores. Well at least it is
    common here in the US, don't know about the rest of the world since HVAC
    isn't as common other places.

    Mike
     
  9. Jim Yanik

    Jim Yanik Guest

    I'm afraid I don't have any answers to those questions.Sorry.
     
  10. Arfa Daily

    Arfa Daily Guest

    The only way that I can see it generating any RFI, is if the joint is not
    good enough to be corona-free. Based on what Jim says at the bottom of the
    thread, removing the lead from the actual CRT does not seem to be the 'done
    thing' - so I'm guessing that there must be a reason for that. Based on that
    assumption, I would still think that it was better to at least try to do a
    good job on a splice initially, rather than risk 'doing a job' on the new
    CRT that left it useless. I would have thought that there is just as much
    potential to do a joint at the CRT end that corona'd and generated RFI as
    there is of having the same happen at a splice - yes ?

    Arfa
     
  11. Meat Plow

    Meat Plow Guest

    I suppose anything is possible. Jim gave good advise on splicing but then
    he's done it a few times.
     
  12. James Sweet

    James Sweet Guest


    Personally I would probably splice the wire then carefully cover the splice
    with silicone, let it cure, and slide heatshrink over that. If the
    connection on the CRT is easy to get to, then solder it there. Cover it with
    ordinary *clear silicone*, not colored, not latex. Let it cure for 48 hours
    before applying power. For the copper tape, any number of glues will work,
    contact cement, spray adhesive, double sided tape, etc.
     
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