Fixing a stuck ceramic trimmer


Actually, the small ceramic trimmers are very easy to clean.  You remove the spring clip that holds the capacitor together.  All you have to do is to use a small screwdriver or small needle-nosed pliers to compress the clip and slide it off of the post that comes from the top section of the trimmer.  You do not have to unsolder the wiring which makes reassembly very easy.

Remove the top and the rubber gasket.  Usually the gasket is "stuck" to the top.  Carefully peel the gasket from the top.  Carefully remove the flat plate
from the top.  You will probably have to use an "X-acto" knife slipped between the top and the plate (or a single-edged razor blade works quite well). Normally just "touching" the seam between the plate and the top will cause the plate to be released.  Do this very carefully so that you don't break the ceramic.  "Freezing" of the plate to the top is the most common problem of these capacitors.  What happens is that when the two parts are "frozen" together the plate turns as well as the top and you cannot ajust the trimmer.  If the assembly turns very far in this "frozen" condition then you loose contact with the lower portion of the capacitor and no connection is made (the capacitor is effectively eliminated from the circuit).

Use alcohol to clean the flat plate as well as cleaning the top and the gasket (you might also use one of the contact cleaners but make sure that no residue is left behind).  Allow to dry completely (about a minute, or so, when using alcohol).  Replace the gasket on the portion that is still attached to the unit making sure that the opening in the gasket allows the spring contacts to come through.

Next put the flat plate on the top with the plating on the plate showing outwards.  Then reinstall top making sure that the center of the plating on the plate makes contact with the spring contacts.  Finally, hold the top of the capacitor in place and turn the unit on its side.  Slide the spring clip back onto the stud from the top making sure that the little positioning "dimple" mates again to the phenolic base of the capacitor and that the clip "locks" into place.

Of course you will have to do a complete realignment of the unt, but 99.9% of the time you will have restored the capacitor and it will function completely normally.

Clean all of the capacitors before turning the unit back on.  What I do is to record the value of the capacitor at each position (there are 2 or 3 values of capacitors used, not just the 8-50) and take all of them apart to clean.  Then reassemble putting the correct value capacitor in the proper position.  You will have to segregate the plates in terms of values as well since they are different between the various absolute values before cleaning.

It takes longer to read these instructions than it takes to disassemble, clean, and reassemble the capacitor.

I have done this to many hundreds of these ceramic capacitors in all sorts of rigs including the S-Line, KWM-2 series, etc.  So far, I have been "lucky" and haven't broken a single flat plate (but, my time is coming!).

Glen, K9STH