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From: Joe Gwinn <joegwinn@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: Predictive failures
Date: Tue, 16 Apr 2024 09:54:40 -0400
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On Tue, 16 Apr 2024 00:51:03 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Joe Gwinn <joegwinn@comcast.net> wrote:
>> On Mon, 15 Apr 2024 13:05:40 -0700, john larkin <jl@650pot.com> wrote:
>> 
>>> On Mon, 15 Apr 2024 15:41:57 -0400, Joe Gwinn <joegwinn@comcast.net>
>>> wrote:
>>> 
>>>> On Mon, 15 Apr 2024 10:13:02 -0700, Don Y
>>>> <blockedofcourse@foo.invalid> wrote:
>>>> 
>>>>> Is there a general rule of thumb for signalling the likelihood of
>>>>> an "imminent" (for some value of "imminent") hardware failure?
>>>>> 
>>>>> I suspect most would involve *relative* changes that would be
>>>>> suggestive of changing conditions in the components (and not
>>>>> directly related to environmental influences).
>>>>> 
>>>>> So, perhaps, a good strategy is to just "watch" everything and
>>>>> notice the sorts of changes you "typically" encounter in the hope
>>>>> that something of greater magnitude would be a harbinger...
>>>> 
>>>> There is a standard approach that may work:  Measure the level and
>>>> trend of very low frequency (around a tenth of a Hertz) flicker noise.
>>>> When connections (perhaps within a package) start to fail, the flicker
>>>> level rises.  The actual frequency monitored isn't all that critical.
>>>> 
>>>> Joe Gwinn
>>> 
>>> Do connections "start to fail" ?
>> 
>> Yes, they do, in things like vias.  I went through a big drama where a
>> critical bit of radar logic circuitry would slowly go nuts.  
>> 
>> It turned out that the copper plating on the walls of the vias was
>> suffering from low-cycle fatigue during temperature cycling and slowly
>> breaking, one little crack at a time, until it went open.  If you
>> measured the resistance to parts per million (6.5 digit DMM), sampling
>> at 1 Hz, you could see the 1/f noise at 0.1 Hz rising.  It's useful to
>> also measure a copper line, and divide the via-chain resistance by the
>> no-via resistance, to correct for temperature changes.
>> 
>> The solution was to redesign the vias, mainly to increase the critical
>> volume of copper.  And modern SMD designs have less and less copper
>> volume.
>> 
>> I bet precision resistors can also be measured this way.
>> 
>> 
>>> I don't think I've ever owned a piece of electronic equipment that
>>> warned me of an impending failure.
>> 
>> Onset of smoke emission is a common sign.
>> 
>> 
>>> Cars do, for some failure modes, like low oil level.
>> 
>> The industrial method for big stuff is accelerometers attached near
>> the bearings, and listen for excessive rotation-correlated (not
>> necessarily harmonic) noise.
>
>There are a number of instruments available that look for metal particles
>in the lubricating oil. 

Yes.  

The old-school version was a magnetic drain plug, which one inspected
for clinging iron chips or dust, also serving to trap those chips. The
newer-school version was to send a sample of the dirty oil to the lab
for microscope and chemical analysis.  There are companies that will
take your old lubrication oil and reprocess it, yielding new oil.

If there was an oil filter, inspect the filter surface.

And when one was replacing the oil in the gear case, wipe the bottom
with a white rag, and look at the rag.

Nobody did electronic testing until very recently, because even
expensive electronics were far too unreliable and fragile.

Joe Gwinn