eacj@batcomputer.tn.cornell.edu (Julian Vrieslander) (11/08/87)
Keywords:ESD, static, Mac II
This may give you sweaty palms the next time you open your Mac II case.
One of our local Apple dealers says that, at the factory service training
sessions, he was told that the Mac II motherboard was *extremely*
sensitive to damage from electrostatic discharge (ESD). Now many of us
already know that CMOS IC's can be damaged by ESD, and take routine
precautions when handling them. The service training instructors
apparently are stressing this in a big way: they claim that ESD control is
especially important around the Mac II because it contains VLSI chips with
unprecedentedly high gate densities (for a PC). To underline this
statement, they told the trainees that damage could be caused by waving a
charged piece of material (eg. plastic film) over the board, or (if you
wear the proper shirt material) by raising your arm.
Apparently, some ESD-induced damage is not immediately evident. One
common damage mode involves an increase in gate leakage current - the
chips function properly until the leakage eventually deteriorates into a
catastrophic failure. The service instructors said that in in a Mac II,
such damage is undetectable at first, but may show up four months later in
erratic program behavior and data loss, possibly culminating in machine
crashes and a bill for a new motherboard. I had heard about such
incipient ESD damage, but never took it very seriously until now.
What to make of this? Well, now that we finally have open Macs there are
going to be a lot of people out there gleefully popping in boards and hard
disks, and most of these folks are not well trained in ESD precautions.
If the boards are as hyper-fragile as the above story suggests, then
there are going to be a lot of IIs coming down with degenerative chip
disease, and a lot of unhappy owners. Apple must know that, so perhaps
the service instructors were being a bit over-dramatic.
But it makes sense to play it safe. Most readers of this group are likely
to be familiar with ESD precautions, but here are some tips for those few
who may not be. With the cover in place and the machine properly
grounded, it is reasonably well protected. You might consider a grounding
floor mat, etc. if there are a lot of static snaps from office carpeting
and chairs. If and when you go inside the case, it is wise to have the
machine grounded (plugged into a grounded outlet), to put it on a
conducting grounded surface, and to keep a grounding strap on your body (I
run a wire with alligator clips from my metal wristwatch band to the
chassis). Move around as little as possible while you are installing
boards, disk drives or accessories and handle them only as much as needed.
Finally, I seem to remember that polyester clothing is more ESD prone than
cotton.
--
Julian Vrieslander (607) 255-3594
Neurobiology & Behavior, W250 Mudd Hall, Cornell University, Ithaca NY 14853
UUCP: {cmcl2,decvax,rochester,uw-beaver,ihnp4}!cornell!batcomputer!eacj
ARPA: eacj@tcgould.tn.cornell.edu BITNET: eacj@CRNLTHRYolson@batcomputer.tn.cornell.edu (olson) (11/09/87)
In article <2853@batcomputer.tn.cornell.edu> eacj@tcgould.tn.cornell.edu (Julian Vrieslander) writes: >sessions, he was told that the Mac II motherboard was *extremely* >sensitive to damage from electrostatic discharge (ESD). Now many of us >... >such damage is undetectable at first, but may show up four months later in ^^^^^^^^^^^ ^^^^^^^^^^^ (with tongue firmly in cheek ...) Is this why the inital Apple warranty is only for 90days? Todd Olson ARPA: olson@lasspvax.tn.cornell.edu ---or--- olson@tcgould.tn.cornell.edu UUCP: {ihnp4,allegra,...}!cornell!lasspvax!olson US Mail: Dept Physics, Clark Hall, Cornell University, Ithaca, New York 14853-2501
agr@vaxine.UUCP (Arnold Reinhold) (11/09/87)
Julian Vrieslander of Cornell U. writes: >This may give you sweaty palms the next time you open your Mac II case. >One of our local Apple dealers says that, at the factory service training >sessions, he was told that the Mac II motherboard was *extremely* >sensitive to damage from electrostatic discharge (ESD). We are an Apple VAR and are marketing an Industrialized version of the MAC II called the AI 90. While we were developing the AI 90 package we had a number of MAC II's taken apart. The mother boards were handled extensively (and I might say carelessly) while we were trying out various concepts. This was in the summer when static is less of an issue, but we have experienced no problems with these initial units. They are now used for development in house. People should *always* follow good ESD practice when handling any computer (our AI 90 production people do!), but we have found the MAC II mother boards to be fairly robust. Arnold G. Reinhold Automatix Inc., 1000 Tech Park Dr., Billerica, Mass. 01821 617 667 7900 Applelink V0280
straka@ihlpf.ATT.COM (Straka) (11/10/87)
In article <2853@batcomputer.tn.cornell.edu> eacj@tcgould.tn.cornell.edu (Julian Vrieslander) writes: >and chairs. If and when you go inside the case, it is wise to have the >machine grounded (plugged into a grounded outlet), to put it on a >conducting grounded surface, and to keep a grounding strap on your body (I >run a wire with alligator clips from my metal wristwatch band to the >chassis). ... WAIT A MINUTE. HERE WE GO AGAIN!!! Do not, I repeat DO NOT EVER ground yourself directly to REAL ground, ESPECIALLY with the machine PLUGGED IN. This can cause DEATH (and quickly!) if you touch the wrong place in the machine. The proper, SAFE way to do it is to connect the ground prong of the machine with an alligator clip or some such means to ground (but do not plug the plug into a live outlet). Then, somehow put ~1MegOhm of resistance between yourself and ground. A well designed static wrist straps has this built in (measure it yourself unless you are sure). The 1MegOhm is enough to dissipate any static buildup, yet keeps you from being a high current path to ground if you touch something you shouldn't. By the way, I try to avoid working on live electronic equipment when I can. When I must, I ALWAYS keep one hand in my pocket (usual;ly the left one). Think about it. The reason should be obvious. -- Rich Straka ihnp4!ihlpf!straka Advice for the day: "MSDOS - just say no."
bob@alberta.UUCP (Bob Gregorish) (11/10/87)
In article <2853@batcomputer.tn.cornell.edu> eacj@tcgould.tn.cornell.edu (Julian Vrieslander) writes: ... <stuff deleted> > >But it makes sense to play it safe. Most readers of this group are likely >to be familiar with ESD precautions, but here are some tips for those few >who may not be. With the cover in place and the machine properly ...<stuff deleted> >conducting grounded surface, and to keep a grounding strap on your body (I >run a wire with alligator clips from my metal wristwatch band to the >chassis). Move around as little as possible while you are installing ...<stuff deleted> An important safety precaution here is to wire a 1M resistor in series with the wire from the alligator clip to ground. It is possible to accidently become a conductive path from a high voltage (ie 110V A.C.) to ground if you touch something you shouldn't. Without the resistor you are taking a VERY big risk. Safety First! Bob Gregorish University of Alberta Edmonton, Alberta
eacj@batcomputer.tn.cornell.edu (Julian Vrieslander) (11/15/87)
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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