I like Gmail; it's easy to quote several e-mails at once...

James:

> I hate to say this, but it sounds to me like either the customer had a
> learning curve on how NOT to use the product that burned through a few
> boards or production did not actually test a batch of outgoing boards.
>
> E.g. it smells like a social engineering problem.

Possible but unlikely.  I've attempted to duplicate this damage through
conditions possible under normal use to no avail.  Plus, both of these
products are fairly mature (one has been shipping since late 2005, the
other since 2001).

Spehro:
>Suspicious, IMHO, that you've seen *no* outright failures from
>this assembly house & run, yet apparently several "latent" failures.
>It's *possible*, of course, but I'd tend to suspect something else
>first and maybe second too.

This was NOT my first choice.  I'm coming to this after about six
weeks of hypothesize/evaluate/discard.  And yes, I do find that
part troubling as well.

>Was it the same customer as well?

There are two distinct products in question here, and two different
OEMs, with failures occurring at many of their customers.

>Symptoms.. latchup, perhaps? Is the power supply entirely internal or
>is it supplied externally or brought out to the outside world? Does this
>mux deal with external signals?

Power supply in both cases is over IEEE 1394.  In one case, 24V, the
other, 12V.  Transient testing to see if I could force a transient through
the input protections bore no fruit.  Symptoms are a 20-40 ohm
short from pin to pin, always from Vdd to Vss and usually from one
pin to another as well.

The mux is completely internal- it takes a voltage from a DAC and
connects it to a 5k resistor divider, OR leaves the high side of the
divider floating.

We have something like 12-13k of these MUX circuits in the field with
no prior reported failures.  Certainly not on this scale.

Mike H.
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