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Help needed with Tek 465 scope disassembly

Discussion in 'Electronic Repair' started by John, Aug 27, 2003.

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  1. John

    John Guest

    Trying to fix my old 465 that's blowing AC main fuse on powerup. Someone
    suggested checking caps on P/S, but to get to them I had to remove the
    trigger generator and sweep logic board first. So far it's been
    straightforward enough, mostly screws and some pin connectors.

    The only things left are two BNC jacks mounted on the front panel that are
    soldered to this board, but I can't figure out how to free them from the
    front panel. Would hate to remove the front panel unnecessarily . Am I
    missing something, or should I just desolder their connections at the board?
    Thanks for your help here. --- John
     
  2. Jim Yanik

    Jim Yanik Guest

    I believe you can just desolder the wire to the BNCs.
    I'd do it AT the BNC.Then you won't forget where the wire gets soldered.
    :)
     
  3. We need to backup a ways here. I've fixed many a Tek 465, and the problem
    has NEVER been a shorted PS capacitor. Many an OPEN or very weak PS
    capacitor, but never seen a shorted one.

    You should be able to determine the problem with the power off and an
    ohmmeter. Just measure across each of the capacitors. and Oh, it could be
    a shorted diode bridge, those were mighty marginal, and a shorted bridge
    could make a PS capacitor look shorted. You may have to unsolder a bridge
    or two to isolate the problem. Which is darn near impossible as they're
    often found mounted flush to the board. Since new bridges are much mor
    ereliable and cheap too, one can just bend the old bridge back and forth
    about 5 times and the leads will nicely break off. Then you can use a
    solder-sucker to suck out the remaining wire and old solder. Then you can
    measure the transformer winding and the filter cap without the questionable
    bridge getting in the way.
    Replace the bridge with a new 3-amp 400-v bridge to give the scope a little
    headroom.


    If it is one of the big PS capacitors, you can usually remove them without
    removing that side board. They're unsolderable from the bottom, and you can
    usually wiggle them out thru the top opening. You'll need a reasonably
    hefty 50 to 100 watt soldering iron to heat up all those wide traces and
    semi-massive capacitor lugs.

    You'll have a bit of trouble finding an exact replacement, they don't make a
    lot of those traditional FP-based caps anymore. You may have to cobble in a
    newer capacitor. It's a bit of a pain, as Tek for some reason depended on
    the 3 ground lugs of the FP capacitor to act as current-carrying conductors.
    You may have to patch in a few jumper wires to restore continuity there.


    Good Luck,


    George
     
  4. John

    John Guest

    Thanks a lot for the detailed info, George, I really appreciate it. I'll
    yank a couple of those bridges as you suggested and let you know how it
    goes. Thanks again. ---John
     
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