In message  <s279c4be.018@mail2.allegro.net> PICLIST@MITVMA.MIT.EDU writes:
> I was working on my old color TV that was a transformer less wonder. I
> forgot to float my scope and when I hooked up the probe ground... POW!
> Vaporized to lead.

It's common practice to remove the earth lead on test equipment, this is far
less dangerous than leaving it connected!. When I do this, I disconnect the
earth lead in the plug and pull it back so it projects ouside the plug, this
makes it fairly visible that the earth is not connected. This is using UK
style 13A plugs, probably the safest plugs around?.

>         If some of you who are new to electronics ever run across one of
> these sets, procede with absolute caution.  They were VERY dangerous with
> the chassis being a floating ground and a 50% probability that mains voltage
> might exist between it and Earth.

The older ones still were even worse, the neutral side of the mains lead
connected directly to the chassis of the TV. If the lead was plugged in the
wrong way around the entire chassis was connected directly to live!. I heard
that the reason for changing to full wave rectifiers was at the demand of
the electricity companies, with an entire street only using positive
half-cycles this tended to pull the mains away from been symmetrical about
zero volts.

Nigel.

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