[Collins] Need Advice - KWM 2A Transmitter Problems

[Glen Zook]

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


--- "Dr. Gerald N. Johnson, electrical engineer"
<geraldj@isunet.net> wrote:

you need to attack the Erie 8-50 trimmers for each
band switch position. They have a tendency for their
internal connection from shaft to terminal (accessible
on the bottom side) to go open.

It is also possible that the ceramic may be stuck
making rotation difficult of impossible. Then
replacement may be necessary.

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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