[time-nuts] Racal-Dana tactile switches

Magnus Danielson magnus at rubidium.dyndns.org
Sun Apr 22 10:21:17 UTC 2012


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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