[Collins] Re: {Collins} S-Line trimmer caps stuck in position

[W7fe at aol.com]

Generally the non-working/stuck trimmers must be  disassembled and cleaned (I 
use alcohol on a Q-tip). This sounds like it  might be tedious, but as with 
most repair jobs, it becomes easier and  quicker after you've done the first 
one.  I've had good luck  doing them in place; that is, not removing the trimmer 
mounting screws  from the chassis.  I just unsolder the leads and push the 
flat  spring/terminal away from the center shaft with a tiny screwdriver or a  
pointed probe.  You'll see that this flat spring is  made with a C-clip cutout 
which fits into a groove on the center  shaft to hold the ceramic sandwich in 
place.  Once this spring is released  from the shaft groove, the pieces will 
drop right out and on to the bench on the  other side.  You'll see how the 
trimmer is made at this  point, what needs to be cleaned, why it didn't vary in 
capacitance  when turned, and how it must be reassembled so it will work as a  
variable capacitor again. 
 
Yes, you'll have to remove the shield cans over the bandswitch wafers to  get 
at those trimmers, and this means sliding the bandswitch shaft out  through 
the hole in the chassis rear apron first....no big deal.
 
One thing to note: Don't apply prying force to separate the sections if  they 
don't release easily. I once broke one of the thin ceramic  pieces while 
trying to slip an Exacto knife between the sections, so I  don't try that trick 
any more.  Patience is the key .... drip a little  alcohol around the edges and 
try to get it to wick inside to dissolve the  internal crud that has caused 
the pieces to stick together. If that doesn't  work, soak the whole sandwich in 
alcohol for a few minutes to free it  up. 
 
I think I recall someone counseling to apply a light film of white  lithium 
grease on the ceramic faces when reassembling. I haven't tried this as  it 
seems to me that the grease might cause more troubles than it will  cure.  I find 
that once cleaned and reassembled, the  trimmers adjust freely but with enough 
friction to keep them in place  when subjected to casual contact or vibration.
 
After reassembly, I use my little Chinese digital capacitance meter to  
verify that the capacitance varies as it should.  Then I solder the leads  back in 
place.
 
It's really not as difficult or as time consuming as it might sound to  
repair these trimmers even if the sections are stubbornly stuck  together, and the 
results are gratifying since they work so  nicely when you are finished.
 
If you do break one, I think Surplus Sales of Nebraska still has some  
(pricey) replacements.
 
73 de Stu  W7FE
Phoenix

 
 
In a message dated 2/15/2008 10:28:48 P.M. US Mountain Standard Time,  
k2dp at charter.net writes:

What solutions have been found for freeing up  S-line trimmer caps that 
appear to be stuck in their present position and can  not be adjusted for proper 
alignment????
 
Thanks in advance & 73,
Dave,  K2DP





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