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Fluke 8375A is not too stable

Discussion in 'General Electronics Discussion' started by (*steve*), May 23, 2014.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    My old Fluke 8375A is misbehaving. This might turn into a repair thread :)

    I think it has been getting worse, but yesterday the problem was so bad the meter wasn't much better than a 3 1/2 digit meter :-(

    The main problem was that with a reasonably high value resistance (10k to 100k) the readings would occasionally be right, but were drifting in the last 2 (and sometimes last 3) digits.

    It seemed to get a little better as the unit was left on for a while, but it was not really useable.

    Oddly enough, occasionally (more often that you could attribute to chance given the +/- 300 or so in the last 3 digits) the reading was spot on.

    My suspicion at the moment lies with the power supply. I'm going to have to take it apart to see if any of these 40 year old capacitors are not as good as new.

    Looking a the documentation for this unit last night, I noted that it has a large number of germanium transistors. *wow*! I sure hope I don't have to replace any of those.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Wow, that's an old meter!

    How many digits?

    Please keep us informed Steve.
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    I suspect its almost as old as Steve ;) haha

    electro swap time, Steve :)

    Dave
     
    Arouse1973 likes this.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, It's significantly younger than me. And it's 5 1/2 digits.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    After opening it up and finding mid 1973 dates stamped on the inside cover...

    1) It's still not as old as me
    2) the power supply capacitors still measure OK for capacitance and ESR
    3) Connecting the guard terminal to the "low" input helps a lot
    4) Pressing the "filtered" button on the front panel makes it even more stable

    Chalk this one up to operator error.

    Oh and it has a resolution of 1uV on the 0.1V scale.

    The zero adjust needs a little tweaking but that's a front panel (via a screwdriver) adjustment
     
    Arouse1973 likes this.
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