Cleaning Ceramic Trimmers

Discussion in '"Boat Anchor" & Classic Equipment' started by KW4H, Oct 21, 2021.

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  1. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Posting this as a separate topic as it could be useful on its own to others -- many boat anchors use these style of trimmers. These four ceramic trimmers are operative, but very touchy and need to be cleaned somehow.

    I've done a little bit of external cleaning on them but am trying to be gentle. What is the best way to clean this style of trimmer capacitor? Is the actual "trimmer" part below or inside the part, or is it entirely the part on top?

    73 - Steve, KW4H

    IMG_5220.jpg
     
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  2. KL7KN

    KL7KN Ham Member QRZ Page

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  3. K6BSU

    K6BSU Ham Member QRZ Page

    These are trimmers. Once set, they require no further attention. "Touchy" is only relative. Depends on the rest of the tuned circuit as to their sensitivity to tuning. The oxidation you see has no effect on operation; the actual capacitor action is between the moving plate and the fixed part. You can't see it and also can't take it apart for cleaning.
     
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  4. AA4PB

    AA4PB Ham Member QRZ Page

    "touchy" is probably due to corrosion on the contact on the back side of the trimmer causing an intermittent contact as you rotate it.
     
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  5. KM1H

    KM1H Ham Member QRZ Page

    Those and other brand trimmers can start acting up with just a light tap. Only long term fix Ive found is a tiny drop of De Oxit D-100, rotate several times and then flush with a quick blast of disk brake cleaner.

    KISS

    Carl
     
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  6. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    Those contacts are silver. The tarnish might be ugly but it's perfectly conductive. Don't touch it.
    --scott
     
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  7. W3RU

    W3RU Ham Member QRZ Page

    If you decide to do disassembly with ultrasonic cleaning, don't leave the parts in the solution for more than about 5 minutes . The silver deposits will be gone from the ceramic parts and the solution will be nice and gray if left in too long.

    Jack W3RU
     
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  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    I just use alcohol. It works just fine.

    No Super Lube dust collecting contaminator needed.
     
  9. WB2GCR

    WB2GCR Ham Member QRZ Page

    Okay... This is what I have found.

    The number of times that these trimmers can be rotated is actually limited.
    What happens is that a combination of voltage and abrasion over time causes the
    thin deposited silver to rub off. Then you see the grey over the surface.

    One needs to be judicious in cleaning, and alcohol is ok.
    Deoxit is probably NG because its (ingredients unknown) ability to "brighten" metals.
    The Silver is hyper thin in reality.

    At a certain point cleaning buys you nothing.
    That point is reached when the silver has rubbed too thin.
    Become porous. Has gaps.

    At this point the trimmer can no longer reach full capacitance, and in fact may not
    have much capacitance at all.

    Before the grey (rubbed off silver deposits) are removed the trimmer was leaky and would
    not adjust properly. After cleaning, if the trimmer's silver is rubbed thin, it still won't adjust
    but will no longer leak.

    The dielectric pad in there is plastic and is rather sensitive to solvents - beware.

    Once there is a grey deposit, best just replace the trimmer.

    Blackened silver is NOT "Silver Oxide" - it is Silver Sulphate!
    Still conductive, but softer than Silver. Silver Oxide is silver colored. We don't see much Silver
    Oxide due to the pollutants in the air, we see mostly Silver Sulphate. Much more in cities than
    out in the country. Fwiw.

    See pix for examples. The one in the picture, even after cleaning was NG. Sometimes cleaning works
    out ok, others not. Be advised. (these were in the cans of an R-390A)

    NOTE: "Silver Dip" is an acid. Glenn did not say this, but one should use a mild solution of baking soda after rinsing the parts, and then another clean rinse or two before re-assembling. The ceramic parts are quite porous! Important to remove acid residue.
     

    Attached Files:

    Last edited: Oct 23, 2021
  10. W1BR

    W1BR Ham Member QRZ Page

    I've seen where silver migration causes the silver conductive coating on the rotor plate to fail open.
     
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