On Mon, 16 May 2005 12:50:22 -0500, Dave VanHorn wrote:

> There is a phenomenon called "soak" where a cap can be shorted, and 
> after the short is removed, it recharges to some level.
> I've seen this in CRTs, where I definitely shorted them out, and 
> later, without being powered, they were able to spark again.

The first colour television transmission I ever saw was in the Science Museum in London when I was 15.  It was 
a "Trade Test Transmission" and it was all about working on high voltage circuits - it demonstrated, by a 
short fictional story, why the acronym  SIDE  is important:  Switch off, Isolate, Dump, Earth.  The Dump part 
is using the resistor probe that people have been discussing, the Earth part is to counteract the situation 
you mention above - leaving the earthing stick (or whatever) connected to dissipate any returning charge.

I'll never forget the part where the engineer was distracted by a ringing phone so made a mistake in the 
circuit (which was big, walk-around style, and very high voltage) and later when it didn't work (and he'd done 
the SIDE thing) was about to touch something that should have been earthed but wasn't, thought about it and 
reached for an earthing stick, and was thrown backwards by the huge Zap that it caused!  It was a very 
effective lesson, and one I can remember in detail over thirty years later - it may even have saved my life 
(since I have always followed it, and haven't had the sort of accident it was designed to prevent).

Cheers,


Howard Winter
St.Albans, England


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist