[R-390] Lightning crashes in audio

[B Riches]

 I have found leakage to chassis is several IF transformers.  Two were from the radio being a mouse house at one time. Others maybe from being stored in a damp location.  To repair I removed transformer. Used a Dremel with a disk and cut away the corner of the base that was holding the connection had dc on it - just leaving the wire free from any part of the base.  Re-installed the transformer and it worked fine.  Be sure to check the decoupling resistors feeding the transformer.
73,
Bill, WA2DVUCape May
    On Tuesday, August 18, 2020, 01:26:33 AM EDT, Stan Gammons <sg063015 at gmail.com> wrote:  
 
 Hi Tisha,

Thanks for your reply and all of the other replies on this topic.

Having a few health issues at the moment, not COVID.   When I get better 
I'll see if I can figure out what is causing the problem and report back 
on what I find.


73

Stan
KM4HQE


On 8/17/20 11:46 PM, Tisha Hayes wrote:
> Mica cap failures have been understood for about sixty years when there
> were unexplained failures in high-reliability applications (subsea
> communications cable amplifiers). There are a variety of failure
> mechanisms, including;
>
> High voltage transients (sometime in the life of the mica cap). This blows
> a tiny little puncture through the mica laminates and eventually---
>
> Silver-ions migrate through this gap
> Carbon tracking from contaminants
>
> Because it is not a constant failure the capacitor gets noisy as this
> microscopic pair of filaments (silver, or carbon or anything else) begin to
> arc over at voltage.
>
> Capacitors that we are dealing with today have had a literal lifetime of
> experiences and any of these may have caused a pinhole in the mica. Also,
> since mica is a mined mineral there are different grades of mica that is
> used in caps. They would classify mica based upon its optical clarity but
> just how many trace contaminants (iron molecules from the geology the mica
> was formed in) or other defects just do not get caught in the mass
> production of capacitors.
>
> *Ms. Tisha Hayes, AA4HA*
>

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