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From: eacj@batcomputer.tn.cornell.edu (Julian Vrieslander)
Newsgroups: comp.sys.mac
Subject: Re: ESD causes degenerative brain disease in Mac IIs
Message-ID: <2924@batcomputer.tn.cornell.edu>
Date: Sun, 15-Nov-87 01:41:23 EST
Article-I.D.: batcompu.2924
Posted: Sun Nov 15 01:41:23 1987
Date-Received: Sun, 15-Nov-87 22:34:46 EST
References: <2853@batcomputer.tn.cornell.edu> <146@cadomin.UUCP>
Reply-To: eacj@tcgould.tn.cornell.edu (Julian Vrieslander)
Distribution: na
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 38
Keywords: ESD, static, Mac II, safety
Summary: IMPORTANT - ignore my original suggestions for ESD reduction


If you read my original posting on ESD damage to Mac IIs, do not, repeat
*DO NOT*, use the techniques suggested in that note for grounding the
computer and your body when working inside the case.  It was correctly
pointed out in follow-up notes by Rich Straka and Bob Gregorish that my
suggestions could lead to serious injury.  I am posting this additional
follow-up just in case there is still someone who read my original message
and missed the notes from Rich and Bob.

When you work on a piece of electronics, your concerns should be more on
protecting yourself than on protecting the chips from ESD.  The computer
should NOT be grounded by leaving the power cord plugged into a power
outlet.  If you run a ground wire to a grounded outlet, make SURE you know
which terminal is true ground.  If you use a ground strap to ground your
body, use a proper one, not an alligator clip on your wristwatch.  The
wriststraps used by service and assembly personnel introduce a high
resistance between your body and ground.  The resistance is low enough to
allow static charges to drain off your body but high enough to minimize
the current that would pass through you if you inadvertantly contacted a
source of dangerous voltage.  Be aware that some electrical components,
especially in the power supplies used for driving CRTs (monitor tubes),
can store lethal voltages for a substantial amount of time after the
device is unplugged from the wall.  Such components are present inside the
small Macs (128, 512, Plus and SE).  If you don't know what these
components are, or how to safely discharge them, you should let someone
else work on your hardware.

Wow, am I embarassed.  It is one thing for me to use quick-and-dirty
grounding methods when I'm stuffing CMOS chips into a "Digi-Designer" box,
and quite another matter for me to advocate those methods to folks who are
going to be reaching into computers and monitors.  That was a real case of
brain fade.  

-- 
Julian Vrieslander    (607) 255-3594
Neurobiology & Behavior, W250 Mudd Hall, Cornell University, Ithaca NY 14853    
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