Greetings, all.  I am enjoying a hearty chortle (more than a chuckle,
but less than a guffaw) over this discussion of electrical power surges.
I have to share this true story:

During my sound contracting days, I had installed some large commercial
power amplifiers in an exercise salon for the disco/aerobics classes.
One day the owner reported that an amplifier was inoperative.  As it was
still under factory warranty, and I did not have a loaner unit for him,
I removed it from service and drove it 30 minutes down the freeway to the
factory for repair.

The chief engineer was available to look inside the amplifier, so he
removed the screws and popped off the cover.  Inside the amplifier, all
chassis surfaces, which were previously anodized black, were now a golden
bronze color, and most of the circuit board surfaces appeared faded.
There were 'shadows' where the previous colors showed through, as if some
high-intensity light source inside the chassis had bleached exposed areas.
The engineer called over other technicians for a look.

After the visage registered for a moment, the engineer quietly exclaimed,
"I have never seen anything like this since working with nuclear reactors
in the Navy!" at which point we ALL took a collective step backwards from
the amplifier and held our breaths! The room was *very* quiet for an age.
...Time passed...

It turns out that the MOV protecting the input mains had outgassed
through a pinhole in the MOV; the material inside the MOV had vaporized,
coating all the surfaces.  Wierd.  When the MOV and fuse were replaced
the amplifier worked fine!

Cheers.  Pete Woodworth¶
Cal Poly, San Luis Obispo, California, USA

 [ I hope the circuit board was cleaned, too.  While the case material
 [ is non-conductive, the MOV itself is a semi-conductor and could
 [ possibly have deposited a conductive coating all over.  -- Robbie