[rescue] SGI goodies anyone?

Carl R. Friend crfriend at rcn.com
Sat Oct 16 21:46:00 CDT 2010

    On Sat, 16 Oct 2010, James C wrote:

> Anyway, if somebody *does* make a critical mistake, they'll learn
> from it, no?

    In some cases, it's a matter if they survive it.  There are bits
in some of the "newer" "old iron" that can be remarkably lethal if
one makes a misguided mistake.

    Switching-mode power supplies come to mind in this regard as they
typically directly rectify mains-power to DC and float it onto
capacitors; the charge voltage on those caps can approach 300 volts
which will be lethal if one is part of the discharge circuit.  Now,
normally, in a healthy PSU there are discharge resistors across
those caps that take them to zero in a minute or so -- but how does
one know if they're not open (infinite resistance) and not bleeding
the caps off?

    There's also the possibility of overloading electrical services
which may result in enough of an overtemperature situation to start
a fire; unless you know your electrician -- and all the ones that
may have worked on your domicile in the last "n" years, or know
your wiring inside and out -- you may wind up with a rude surprise
after a few hours of playing with your latest acquisition.  It's
worth noting that the fire will likely not originate at the outlet
in use or at the distribution panel; if there's more than one outlet
on a circuit, it might very well start at any one of the necessary
junctions in said circuit.  Do you know where they are and what
shape they're in?  Where any loose splices might be?

    Those two situations -- high-voltage/high-current shock and
fire -- are the biggest threats, but others exist as well, especially
if one is working with *really* "elder gear".  The amount of force
exerted by a head-carriage on a removeable disk-pack drive in
emergency-retract can, if one is very unlucky, amputate a finger.
If one has long hair and is working with rotational machinery of
any sort, tie it up; the same goes for loose clothing.  Low-voltage/
high-current can be a problem if one's watchband gets welded to it
whilst a machine is energised.  And in extreme instances, components
can eject junk that can harm eyes.

    So, yes, "that which does not kill us makes us stronger".  But,
it's better to do one's research up-front to avoid the former.

    To crib a line, "Let's be safe out there."

| Carl Richard Friend (UNIX Sysadmin)            | West Boylston       |
| Minicomputer Collector / Enthusiast            | Massachusetts, USA  |
| mailto:crfriend at rcn.com                        +---------------------+
| http://users.rcn.com/crfriend/museum           | ICBM: 42:22N 71:47W |

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