[R-390] Z503 Replacement

[Randy and Sherry Guttery]

On 4/4/2011 6:15 AM, Stephen M. Murphy wrote:
> That's what I was wondering, whether it is a manufacturing defect or an
> upstream failure causing the problem, since these things typically don't
> (can't) just fail on their own.
While your statement is true in the strictest sense, 
sometimes the cause of failure is so obscure as to appear 
"without cause".  As far as a manufacturing defect, yes -- 
if you consider not having a crystal ball, not designing for 
a life time in excess of 50 years, etc.

Here are "common causes" of winding failures:

1) aggressive flux literally "eating" the wire.
2) potting material being / becoming so stiff as to un-duly 
stress a wire until it fails
3) leads being so short such that the wire suffers from 
strain (thermal cycling, vibration, etc.) - leading to 
eventual failure
4) damage during assembly /  repairs - nicks, etc. that 
weaken a wire at a connection point.  This why heat or 
chemical stripping is often preferred as opposed to 
mechanical scraping.
5) non-uniform wire - thin spots, etc. that eventually fail.
6 external component failure - literally overloading the 
wire's capacity such that it fails.

Most of these coils are wound with very small gauge wire - 
and even when litz wire is used - it's resistance to damage 
is quite modest.
>    I'm also wondering if it's an "across
> the board" problem, or just affects those radios that were subjected to
> outdoor storage.

This is across the board as you say - as it is common in 
"civilian" radios as well as military, and while exposure 
isn't good - if there isn't a "flaw" that such exposure 
stresses...   exposure isn't a "guarantee" one way or the 
other (i.e. an exposed radio might not have any such 
failures - while a radio that has been sheltered all it's 
life might have some winging somewhere fail.

.02

-- 
randy guttery

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