On 04/22/2012 06:41 AM, Charles P. Steinmetz wrote:
Stewart wrote:
It's a design fault and eventually all of them will fail.
I'm not convinced of that. There has been substantial discussion of
Racal switches on the list in the past, and I suggested at one point
that the failure mechanism (dry, cracked "rubber") could be related to
the counter manufacturing process -- in particular, soldering and/or
cleaning of the front panel PCBs. In my experience with 1992s (quite
extensive), I have found that (i) in some counters the switches never
seem to fail, while (ii) if one switch fails in a counter, all of the
others are not long for the world. There does not (IME) appear to be any
correlation with the color of the switch body or the markings on the
switches.
Then again, I suppose making switches that won't survive every possible
abuse during whatever soldering and cleaning processes a customer might
use could be considered a design fault....
This is not uncommon.
I know that one large telecom manufacture had problems with a known
crystal oscillator manufactures OCXOs. What the telecom manufacture
didn't know was that the crystal oscillator manufacture had installed
temperature guards into their OCXOs, so when they did most-mortem they
could pin-point the error to overheating in the śoldering process.
Even if the soldering requirements where clearly stated, the wave
soldering process overheated the OCXO. When they moved over to hand
solder in the OCXO the failure rate went away.
The failure mechanism you describe would then have a longer time before
it hit widely, so the learning process will be longer. Maybe some will
even think it doesn't even care if they fail after 15+ years. It's only
the time-nuts that suffers...
Cheers,
Magnus
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