Smoke on the Horizon... oh s**t!

From: John Lawson <jpl15_at_panix.com>
Date: Mon Feb 16 14:29:22 2004

  OT but relevant:

In the late 80s I worked for a well-known (but not having any 'D's in the
name) manufacturer of theatre audio gear. We shipped an order to a
multiplex in the Gold Coast of Australia. These devices were made up of
several medium-sized boards, which were assembled at a board house and
then tested, repaired, and burned-in by us prior to system assembly, final
test and cal, and ship. All OK.

  It was our design practice to put a 1 Ohm resistor between the rails
and most of the audio opamps, generally a 1/8W unit. Also they ICs were
all decoupled properly with 1uF caps, from the IC Vss pins to ground.

  The order was for 10 screens of a 14-screen multiplex... we burned the
systems in for 24 hours, gave them our blessing, and out they went. The
contractor in Australia installed them, tested them, all ok. The theatre
was set to open on a Monday evening, and sometime that Thursday (Aus time)
morning, a generous quantity of the tantalum decoupling caps failed
shorted across the bipolar 18V rails. Of course the 1-ohm resistors joined
the fun by becoming incandescent and buring holes in the boards, thus
filling the projection room with expensive, tragic smoke.

  Not being the first occurence (just the all-time worst) of this failure,
we assembled 10 new systems by hand, tested 'em, and I flew them from LA
to Sydney and installed them - got it done as patrons were seating
themselves in the theatres. After staying the night to make sure that
all available fireworks were spent, I flew back, having spent nearly 100
hours awake and very very busy. I don't even remember the return flight -
I was asleep as sson as I sat down.

  We tried to sue the distributor of the parts, but they said "...yawn...
yeah, right, manufacturer is in Taiwan... go ahead... see ya in ten
years..."


  Thus ended the saga of the 'Blue Bombs', since that was their body
color. Until they exploded.

  After that, just mentioning the word 'tantalum' could get you fired.



  Cheers

John.
Received on Mon Feb 16 2004 - 14:29:22 GMT