Ceramic Trimmers & R-390s

Discussion in '"Boat Anchor" & Classic Equipment' started by WB2GCR, Feb 10, 2019.

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  1. WB2GCR

    WB2GCR Ham Member QRZ Page

    Sherlock Holmes & the R-390

    Applies pretty much to ceramic trimmers in general, I expect. (This is the redacted and short version)

    Three R-390s fell out of the sky. None were in working condition. After quite a bit of effort the #1 unit was demoused and made to work. Then the plan was to determine the condition of 2 & 3.

    By swapping known good modules out of #1, both 2 & 3 were made to play. Since the RF deck on #3 was very clean, but the front panel looked like graham crackers in milk (severe aluminum corrosion) the plan was to swap a fresh front panel... but. The "but" was that the chassis on the 390 does NOT have removable side panels, it's all one unit. That left making #2 "the" unit. The side panel on one side had corrosion too.

    Unit #2 was fired up. All good. Except. Deaf on 4mc, 5, 6 and 7. Found the burnt up 1st can, the ANT tuning can. Pix were put up earlier. That should fix it! Nope. Cans 2 and 3 peak, but the can to the rear does not peak at all. It's one of two between 1st RF amp and 2nd RF amp, actually the 2nd.

    Sherlock said, swap a can from the other deck! Swapped the can...still didn't work! what's the probability of the same can from a different deck, made by a different manufacturer in a different year not working!! Just about nil.

    So, obviously there's a flaw in that RF deck that had been transmitted into enough to char that RF input coil. After all the scope and DVM checks I could figure out, the plan was to swap the RF decks. A warm 50 degree winter day meant that i could degrease the gummed up #3 gear train and swap it into #2.

    After swapping it in, which went rather well, plugging in the cans, turning it on... ahhh! Nah. It still didn't work, deaf on the same bands. Believe me, everything was checked.

    Last resort - took ALL the cans out of that row from the #1 unit, removed all the cans in the row from #2, and tried it again. SUCESS! But... huh? Really? So that meant, bad cans from two different RF decks!!

    Later, after a whole lot of swapping of cans, testing, and the like - did I mention that I replaced the two silver micas in one of the cans? Still didn't work!

    What did that leave? Yep, the TRIMMER!

    I was able to dissassemble the trimmer and found that the silver had spread across the two ceramic surfaces. Contact cleaner took most of it off. I've tried an cleaned two cans. One returned to proper operation. The other had been lubed with PTFE spray lube, and did not. I may clean it again and retry.

    Attached Files:

    KA0HCP likes this.
  2. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page

    KA0HCP likes this.
  3. WB2GCR

    WB2GCR Ham Member QRZ Page

    Glen, K9STH

    good write up.
    I noticed that I could not find a picture of the cleaned surfaces??

    I used contact cleaner. No known residues. Dunno what Harbor Freight
    uses in their bottle of "stuff". I'd worry about residues. But probably it's

    Glad to find that I'm not the only one with bad trimmers.
    I now suspect strongly that the 1st mixer in my KWS-1 is suffering from
    the same malady! I'll be pulling them shortly.

  4. K8ERV

    K8ERV Ham Member QRZ Page

    You sure are lucky you didn't get hit by one when it fell out of the sky.
    They are a mite heavy.

    TOM K8ERV Montrose Colo
  5. WB2GCR

    WB2GCR Ham Member QRZ Page

    Nyuk, nyuk, nyuk... :D

    The best part was the soft landing, no mangled metal! :D
  6. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page


    I would bet that well over 50% of the S-Line and KWM-2- series equipment have at least 1, and probably several, of the ceramic trimmers frozen and an even higher percentage in the older Collins equipment.

    I always rinse the components after ultrasonic cleaning. The powder works fine for cleaning jewelry and other things. However, I do rinse everything in water right after the cleaning is complete.

    Glen, K9STH
  7. WB2GCR

    WB2GCR Ham Member QRZ Page

    Frozen was not the issue here, but I expect that it is an issue.

    My problem was non-frozen, and non-peaking! :D
    Well, now I know...
    ...I see trimmers being removed and cleaned in my future!
  8. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page


    Frozen and migrated plating often go hand in hand!

    I have found that cut off acid brushes work very well when scrubbing off the migrated plating.

    Glen, K9STH

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