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Schematic for Tek P6137 scope probe?

Discussion in 'Electronic Equipment' started by Joerg, Mar 29, 2007.

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  1. Joerg

    Joerg Guest

    Is there a schematic for that probe somewhere on the web? Or does
    someone know what would be a good replacement for the main calibration
    variable cap it there? It's the red plastic one, SMT, square.
     
  2. Phil Hobbs

    Phil Hobbs Guest

    I'd measure the capacitance on the scope end, add 10 pF for the scope,
    and then divide by 9 to match the voltage divider. That of course
    neglects other capacitance in the circuit, but for a trimmer it ought to
    be reasonably close.

    Cheers,

    Phil Hobbs
     
  3. Joerg

    Joerg Guest

    Yes, I'll probe it out if there is no schematic. But these things are
    way more complicated. IIRC there were several other trim caps and three
    potmeters or so in there. Plus some fixed value SMT components. The
    gold-plated BNC as well as the tip cable are clicked into slip ring
    holders. Quite impressive, actually.

    At least I was able to finish the measurement by wedging a piece of
    toothpick in there. Not so with the baseband analyzer. It had been
    literally destroyed in shipping. Wanted to measure phase noise on VCSELs
    but I guess that has to wait now :-(
     

  4. I thought that the color of the variable capacitor's body told you
    its range? I've seen charts that told which color was what range, but
    its been a few years.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  5. Joerg

    Joerg Guest

    No idea. I am used to ceramic trim caps where the range is printed onto
    the base. But on my designs I never use any of that, it's all electronic
    auto-calibration so I haven't kept up with the fashion trends ;-)
     
  6. Tom Bruhns

    Tom Bruhns Guest


    Might it be one of the muRata TZV4 series? Have a look at DigiKey
    490-1980-1 and 490-1981-1; slightly different lead configurations of
    the same thing. 20pF max, 4.5pF min, N750 tempco.
     
  7. Joerg

    Joerg Guest

    Thanks, Tom. Those look a bit larger but could possibly fit. Next time I
    am at that client I'll unsolder one and measure it.

    The 2nd P/N datasheet link resulted in an invalid part number. But that
    isn't anything new at Digikey. After they botched the search engine last
    time it hasn't been the same. There are times where just waiting a few
    hours fixes a link, then the next day it's broken again.
     
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