On Monday, December 8, 2003, at 01:31 PM, Stephen wrote:
You win the Eudora 3 Chili Award of the week!
Antonio Rodr�guez wrote:
I have several friends that are either electronics hobbyists, or that even
work as repairmans. I have heard several stories about shocks by high
voltage discharges from large tubes (more than 20"), and the worst thing I
have heard to have happened is a friend of mine being inconscious for half
an hour.
Your friend is very lucky to be alive.
Taking into account that big CRTs have an anode tension that is
three to four times higher than the present in compact Macs (some big TVs
carry more than 30.000 volts!), I would say that you aren't in a big danger
when you are working with an (undischarged) compact Mac. To that you should
sum that about half of the compacts ever manufactured provide an
auto-discharge circuit, and that even in those that doesn't provide with it,
you ussually don't need to get your hands near the high tension parts of the
analogue board or the CRT.
It's hard NOT to get near the potentially hazardous parts of a compact Mac.
Replacing the high voltage circuitry was the most common repair I did on
compact Macs (except adding RAM - not really repair) and this was usually
accomplished by just replacing the whole analog board. Normally I'd let them
sit for a day and discharge by themselves, but on occasion would have to
manually discharge them before working if someone was in a hurry. I don't
know the actual amperage, but judging by the spark you could generate, it
was a pretty healthy (or unhealthy as the case may be) amount.
Sorry, but that is hogwash. As anyone who has ever played with Vandegraaff
generators or Tesla coils (the later being much more dangerous) can attest for,
voltage alone doesn't mean anything. Vandegraaff generators can certainly
generate extremely impressive sparks, but deadly they are not.
Static electricity you build up by shuffling over your carpet can approach the
same voltage range these tubes use, but unless your heart is extremely weak
I doubt you would die from it.
The capacitance of the tube (which determines the amount of electrons
(read amperage) which are available to zap you) depends largely on the gap
and the size of the plates. Since the plates are interior and exterior surface
of the tube, a 9" or 10" tube would pack a tiny amount of wallop compared to
say a 30" tube.
Jens Petersohn
P.S. Voltage and current ARE NOT related other than by specifics of a circuit.
Current is the quantity (more or less) of electrons passing and voltage the
energy per electron. (Volt = Joule/Coulomb, Ampere = Coulomb/sec).
But I can't say that 100% for sure, so take this advice at your won risk,
etc. <--- "cover your ass" sentence.
Anything with mains power going in is potentially dangerous (read deadly)
and has to be handled with respect.
Stephen
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