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Exploring rotary encoder problems

Discussion in 'Electronic Repair' started by N_Cook, Sep 21, 2011.

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  1. N_Cook

    N_Cook Guest

    Deeper than just saying clear out the grease. 2 in 2 days, first input
    selector of an amp , not explored in depth, second vol control of a music
    centre.

    First had radial contacts that were slightly staggered and the fixed
    contacts were in line , second was exact radial contacts and staggered fixed
    contacts. On the second I took some R measurements before and after.
    There are 3 contacts, one common and the other 2 staggered to pick up CW or
    CCW rotation. Just measuring between the 2 sense contacts as at some point
    they are cross connected, measured 2.5R each of the posistions but very tiny
    position to get this reading. Ladled out and then dissolved the grease,
    reassembled and took readings again . Now 1.5R each bridging posistion and
    a lot easier to find that posistion, ie more latitude. I imagine from the
    consistency of the R readings that something to do with deforming or block
    under one of the contacts reducing the contact to a very small area and then
    only marginal connection posistion bridging the 2 contacts. I assumed the
    electronic sensing was one line before the other but perhaps duration of
    both contacts on simulataneously, or not, is also something to do with
    normal sensing
     
  2. shrtrnd

    shrtrnd

    3,826
    520
    Jan 15, 2010
    Usually just dirty contacts. Interferes with the connection to the contacts.
     
  3. Clean the moving contacts and stationary contact area as you would relay and
    switch contacts. Better to replace the control, but this will fix it.

    Mark Z.
     
  4. N_Cook

    N_Cook Guest


    I've never seen a relay with grease it it. Rotary encoders or the BCD type
    ones, it is the grease thats the problem but exactly why it is a problem is
    still not fathomed. I assume a hardening or accretion process that
    eventually wedges under a wiper. Why do they not use "dry lubricant" perhaps
    locksmith's graphite as long as in a minute quantity.
     
  5. N_Cook

    N_Cook Guest


    I can see that with multifunction DVM rotary dials where there is small gaps
    between tracks. But the 2 rotary encoders I looked into this week were about
    1mm wide spokes tracks with the contacts at the periphery so spaces of about
    5mm of insulator disc material
     
  6. N_Cook

    N_Cook Guest

    What was the spacing between pads on those CATV units? The pads or tacks in
    these switches were about 5mm. As far as I can tell the problem was not
    metalisation smear over the insulated gaps but a problem while in pad
    contact. No visible smearing of metalisation seen on either switch. These
    pads are just like spokes of a wheel and once the problem started it is much
    the same around the whole disc, not specific to one or two positions
     

  7. The problem on rotary encoders is not so much the grease, although I believe
    that is a contributing factor.

    Every encoder I've seen with this problem suffers from tarnished contacts.
    It's obvious, and you can tell by a simple close inspection. Just like a vcr
    rotary mode switch. Clean with a fiberglass brush and De-Oxit. Repeat the
    process. Turns tarnished metal clean and bright.

    I still favor replacement when possible.

    Mark Z.
     
  8. N_Cook

    N_Cook Guest


    I'm still going with a mechanical grease problem. If it was tarnish it would
    have to be tarnish on a sprung contact as once erroneous it is near enough
    the same problem on all spokes of the disc. The hardening grease is also in
    the shaft area and puts up noticeable resistance to turning, the first
    indication it is a grease problem. I first came across the grease problem on
    sub min mixer pots that are more the size of presets. The wipers are made of
    such fine metal it takes little compaction of the grease to get under them,
    the resistive track is fine no wear at all .
     
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