Re: {Collins} Tough problem in 32S-3 (still)



I have replaced that feed through several times on S-3 and KWM-2 rigs and while it is somewhat difficult....
Removing the band switch shaft and the rear cover is not hard...most of the rigs I work on have these covers off and on so much that they need zippers installed.
Be sure to get the orientation correct on each band switch when you put the shaft back in!

The coax on top can easily be removed without removing the slug rack....raise the rack all the way up.
Just take your time, remove the adjacent tubes and replace that thing.
I know for sure ad so does Tom....that this feed through can cause some very weird instability and unusual problems.

But....before you replace it.....check to see if the unit has ALC on any other band.
That feed through can go frequency sensitive and act very squirrely and also cause PA instability problems.
If you know the PA is unstable right now.....for sure you will have to replace C62 anyway.

That cap may change value....BUT....the usual fail mode is it goes to intermittent ground in operation....causing all the hell.
You cannot measure the ground with a meter...this is one of those things that comes with bench experience with these rigs.

Have the diodes been replaced??
One time I found a diode that was marked backward....someone else replaced the diodes and of course it would not work....
Now THAT was hard to find....for me anyway.


73

David Harmon
K6XYZ
Sperry, OK

-----Original Message-----
From: Collins [mailto:collins-bounces+k6xyz=sbcglobal.net@xxxxxxxxxxxxx] On Behalf Of Grayson Evans via Collins
Sent: Sunday, August 4, 2019 12:34 PM
To: Tom Hankins <thankins@xxxxxxxxx>
Cc: collins@xxxxxxxxxxxxx
Subject: Re: {Collins} Tough problem in 32S-3 (still)

Well, I also thought it was a bad C-62, but there are a couple of problems with that idea (I think anyway).

The problem with the C62 theory is it is connected directly to the grid drive line to the finals.    If it went high in value enough to kill the AGC, it would also kill the grid drive, yet grid drive is fine, the same as my other 32S.

The practical problem is that cap would be a real bear of a pain to replace or even just disconnect.  It is very hard to get to, inside one of the band switch cans, plus it has 8 connections on one side, some from the fine wire on the coil forms, and a coax connection on the top that is very hard to get to.  Have to remove the slug rack.

Even if I knew it was C62, I don’t think I would attempt to replace it unless I could come up with a strategy to replace it without damaging other parts. 

If I think of something, I’ll let you know.
72, Grayson KJ7UM

> On Aug 4, 2019, at 10:59 AM, Tom Hankins <thankins@xxxxxxxxx <mailto:thankins@xxxxxxxxx>> wrote:
> 
> Hi Grayson, sounds as if your problem may be C-62, the feed trough cap. Is there a way to disconnect both ends and use anther regular cap to provide the voltage wit out messing up the neutralization or grid drive. I don't currently have an S-3 or I would take a closer look for you.
> Tom H
> K0EOA

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