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Old Avo 8

Discussion in 'Electronic Repair' started by Ron(UK), Apr 11, 2005.

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  1. Ron(UK)

    Ron(UK) Guest

    Hi folks

    I have an old but much loved AVO Model 8 which was my fathers before he
    passed on. It has little monetary worth, but great sentimental value. We
    both used this meter for years in our business.

    Sometimes the needle only reads about half the deflection it should for
    a given input, a tap on the case usually puts it right temporarily, but
    I`ve spent hours searching for a dry joint or bad connection. Typically
    the fault never occurs with the meter out of it`s case.

    I wonder if anyone has experience of this problem? could it be the
    movement itself? any clues?

  2. Could it be a static charge on the cover? I have seen this to be an issue
    on some meters, especially if someone wipes dust off the surface.

  3. Ron(UK)

    Ron(UK) Guest

    Yeah I have a Phillips analogue meter that does that a lot, rub the
    plastic "lens" over the movement and the needle rises, to settle again
    some time later.

    My problem is definitely electro/mechanical in nature.

  4. Is it in the meter movement itself? Sometimes, stuff flakes off of the
    metal yoke and is attracted ib between the moving coil and the surrounding
    piece to produce intermittent sticking.

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  5. Ron(UK)

    Ron(UK) Guest

    I cant see anything, the needle doesn`t jam or stop suddenly. It`s as
    tho there`s some kind of increased electrical resistance in movement
    somewhere, and a gentle tap gets it right again for a while, I thought
    maybe it was one of those common things that everyone knows about but me...

  6. Hi Ron

    ISTR that some AVOs had a 'divide scale reading by 2' button - could
    that be faulty / intermittent. Or maybe my memory's faulty ????!

    Suffolk UK

    ======return email munged=================
    take out the papers and the trash to reply
  7. NSM

    NSM Guest

    You can eliminate that by wiping the glass with a cloth damped with water
    with a little dishwashing liquid. However IME it's dust or dirt in the
    magnet gap. You may need to find a good meter repairman.
  8. Barry Lennox

    Barry Lennox Guest

    We had hundreds of them in the Air Force, and that was a known fault,
    not common, but not rare either. Fixed by movement replacement, and
    that was the major reason for getting rid of them, the spares became
    outrageously expensive, ie you could purchase a lower-end Fluke for
    less than an AVO movement.

    Barry Lennox
  9. ;-)

    You can still buy a new Model 8 Avo. About 600 gbp.
  10. NSM

    NSM Guest

    Holy crap in a bucket! I still have a Salford 50 Super Selectest which is
    much nicer looking but it's movement sticks too now. However you can buy
    those used for about US $50.
  11. James Sweet

    James Sweet Guest

    Try gently tapping each component with a stick while watching the meter, you
    may have a resistor with an internal break or an invisibly cracked solder
    joint, happens sometimes.
  12. Bram Stolk

    Bram Stolk Guest

    If it ain't static, it could be just friction in its pivots, normally
    tapping with a pencil on its glass shall free the needle. If you are sure
    the problem is not in the meter movement it must be one of these
    series/shunt resistors which is common to all meter ranges. Is your problem
    persistent on all ranges and functions/Ohm/VDC/VAC/Amp ? Is your problem
    independent from needle deflection ? e.g at full scale/half scale/quarter
    scale ?

    Is your meter still properly balanced, i.e. reading does not change when
    meter is rotated or tilted ?
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