TV-OUT on laptop causes major damage, fire / shock

[Duane Attaway]

On Fri, 3 Dec 2004, Brian Densmore wrote:

> Well it depends on the type of capacitor. It would have to be a 
> polarized capacitor. I remember when I used to test power supplies for a 
> company I worked at. We would buy them for our products, but they needed 
> to be tested before being installed in our equipment. Every once in a 
> while a PS would have the capacitor in reverse polarity. Quite a show 
> when a big capacitor blows. Less frequently the capacitor would take too 
> much voltage with the same end result, explosion. why do you say it 
> would have to be instantaneous? Although from the description of the 
> event it was instantaneous.

I'm pretty sure its going to take a few moments of current to start 
melting the plastic like that.  Capacitors release their energy too quick.

I haven't been able to make a capacitor uniformly melt a jacketed wire. 
The wires would quickly vaporize at one point, leaving the plastic intact 
except for a small hole.  At my last job we used a capacitive discharge 
device called a "thumper" to locate bad cable sections.  It would 
discharge up to 15 kilovolts from a 15uF capacitor and thump a hole in the 
bad section.

Just for kicks long ago, I hooked the thumper up to a 40 watt fluorescent 
light one time.  The light appeared to lift off the ground before 
exploding into dust.  That thing made a violent self cleaning bug zapper 
too.

Oh, did I mention that the wire was dancing?  It was pretty cool...

I believe the seperate video inputs of his television use switching diodes 
to select what video is live.  I believe the current shorted the diodes, 
so all the inputs stay on.  If I remember right, these boards cost $50, 
but only cost $1.00 to fix.  But we have a warranty in this case to keep 
us out of trouble.

I love post mortem troubleshooting.  When things go bad, its fun to see 
what exactly went wrong and keep it from happening again.  Sounds like 
they had a design flaw which they later corrected.  So we may have a happy 
ending out of this.