Conference 7.286::macintosh

>     What does a grounding strap cost at Radio Shack?  Does everyone out
>     there use them?

I can't help with the Radio Shack price, but I recently bought one mail 
order for $5.95 from APS when I upgraded a disk. I'd expect the Radio Shack 
price wouldn't be much higher (and, hopefully, not much lower :^).

    I cheat lots of times and do not wear a strap.  But if I'm writing up
    something for someone else to follow, I don't want to suggest unsafe
    zapping to them :-)
    
    Initially I didn't even own one, but sometimes I would take a long
    chunk of wire and run it under my watch and the other end to a grounded
    surface.  But then one day I saw a grounding strap in Radio Shack for a
    few bucks (I forget how much but under $10).  I figured I should get
    one and then I wouldn't have to worry.
    
    The thing to worry about is a static discharge between you and the
    SIMM/DIMM you are going to install as you are picking it up, or as you
    approach the motherboard with the SIMM/DIMM, a spark arcs between the
    SIMM/DIMM and the motherboard.  This can destroy some of the chips.
    
    I almost never wear a grounding strap when playing with disk drives,
    but the samethings could happen to them.  I'm just luckly.
        
    As for your friend, I do not think a grounding strap would have changed
    anything.  Static discharges then to fry chips, not mess them up just a
    little but everything is OK.  But then again, if you get a grounding
    strap, you can eliminate one aspect of guilt :-)
    
    I guess the best rule of thumb is: 
    
        If you just kissed your wife and sparks fly, don't handle
        ungrounded electronic equipment!
        
        				Bob Harris

> Initially I didn't even own one, but sometimes I would take a long
> chunk of wire and run it under my watch and the other end to a grounded
> surface.

For those out there who are thinking about doing this (and I've done it, too,
although for me it was with alligator clips :-), the reason a grounding strap
is better is that it has a high resistance so it can't fry you if you
accidentally connect it to something that isn't ground (or accidentally touch
something that isn't ground with your other hand).

A static discharge that you can't even feel can wreck the I/O drivers on a CMOS
chip (which is most chips, nowadays), either one on the motherboard or one
you're installing.  A grounding strap is cheap protection.

-Doug

    I recently added memory to my Performa also.  I wore a grounding strap.
    I clipped it to the chassis on the machine.  Of course, afterwards I
    realized that I had unplugged the machine from the wall so I was
    clipped to a machine that itself wasn't grounded. :-)  At least I
    was at the same potential as the machine.
    
    Anyway, to the real point, afterwards I too noticed the sound wasn't
    as loud as before.  On my Performa 575 (.0 didn't say what kind of
    machine he was updating), the motherboard plugs into a connector
    in the front of the machine that provides connections to the volume
    control, the speakers, the SCSI connection to the internal disk
    and CDROM. etc.  I think the electrical resistance in the connector
    may have changed (gotten higher with corrosion or something) and thereby
    lowered the sound quality.  So far, it hasn't bothered me since I
    always felt that the lowest sound level was still too loud for me.
    Everything else has worked but I think everything else is digital,
    not analog like the speaker volume.
    
    You might want to back out the motherboard and clean off the edge
    connector.  I don't know how to get into the machine and clean the
    connector inside.  Long q-tips?  That might leave fibers inside that
    might haunt you later.  Anybody else with suggestions?
    
    				-John

>    Anyway, to the real point, afterwards I too noticed the sound wasn't
>    as loud as before.  On my Performa 575 (.0 didn't say what kind of
>    machine he was updating), the motherboard plugs into a connector
>    in the front of the machine that provides connections to the volume
>    control, the speakers, the SCSI connection to the internal disk
>    and CDROM. etc.  

    YES..I too was putting it into a Perforam 575.  I pulled the mother
    board from the back, swapped the 4MB Simm for the 16, and plugged
    it back in.

    It actually was a week later that she called about the sound, again
    musing about the lack of the grounding strap.  So when the Hard Disk
    Repair and the re-installation of the OS seemed to bring it back
    (although maybe not as loud as before) I left well enough alone.
    I wanted to pull that board and look at the connectors...but I was
    sure THAT TIME I would blow something.

    I wonder if this is a problem with the 575?
    bob

Pedantry alert!

The kind of static electricity shocks you feel after sliding
over a car seat or walking across a carpeted floor are the result of a
static charge that can develop 10,000 to 50,000 volts of potential.
The insulating material inside a computer or memory chip is designed 
to withstand potential differences of as little as a few volts, or 
about 4 orders of magnitude less voltage.  The total stored charge is
small by human standards, that is, there's not enough stored charge to
produce enough current to do any damage to a person.
However, there's enough so that it all goes at once, resulting in very high
current for a very short time.  Inside a chip, this means that there's enough
voltage to cause the insulation to fail, which allows current to flow, 
with enough charge to generate enough current to dissipate enough power 
to melt or vaporize part of the chip.
(Here's the first three years of your BSEE in one compound sentence:
  A voltage difference is created by separtion of charges, plus and minus;
  the flow of this charge is current, proportional to the voltage and
  inversely proportional to the resistance; power is the product
  of voltage and current; power is disspated mostly as heat.
  (You get the rest of the details during senior year.))

So why a grounding strap?
You WILL accumulate static charge just walking around.
Your feet rub against the floor, your slacks rub against your legs,
your butt slides over a chair.  For some reason, friction induces separation
of charge, especially between susceptible materials (leather and cloth,
plastic and fur/hair, etc.).  VERY LITTLE FRICTION IS NEEDED TO INDUCE 
A LARGE SEPARATED CHARGE!
The grounding strap allows the charge to flow in a controlled channel,
reducing its buildup, eliminating the voltage and preempting high current flow.

So, should you use a grounding strap?
Well, I don't, and I handle memory and other hardware components
on a fairly regular basis.
What do I do instead?  I ground myself or dissipate my charge by touching
large hunks of metal on a regular basis, especially before I have to touch
an isolated component, like a SIMM lying on a bench.
DON'T SHUFFLE YOUR FEET or SLIDE AROUND ON YOUR CHAIR while working 
on the materials at hand.  See the capitalized text above and think about
how big a charge you accumulate sliding 12 inches across a cloth car seat
while wearing a leather coat (or wearing a cloth coat and sliding across
a leather seat).

Did the base noter do any damage to the system he was adding memory to?
Sounds like no.  Had there been any static induced damage, it's likely that 
it would have been permanent and more substantial than reduced volume
at the speakers.  Did the disk problem result from static?
Possible but rather unlikely.
Was his friend right to be concerned about his lack of grounding?  Probably....
Will I buy a grounding strap?  Probably not....

- tom]

(My daughter blew out the front end of my hi-fi receiver once by touching
it and discharging a static charge.  Total loss to the electronic controls
on the front panel, but I didn't make her wearing a grounding strap
the next time she wanted to play a CD (with the new receiver).)

>                      <<< Note 951.6 by REGENT::POWERS >>>

I agree with everything you say, except that I'm thinking of buying
a grounding strap just to make my friends feel better....

I also dont think its necessary, but it'll make them feel better (and
make me look EVEN MORE like an expert!!)

I can see how a grounding strap would help when its connected to the chassis
of the machine and I reach in and remove a Simm...but I dont see how
it works when I then reach over and pick up that Simm lying on the bench.

I also dont walk around much after discharging myself and getting
to work...great advice.
thanks
bob

    Industrial strength repair centers do not wire up each of their
    technicians' wrists to ground.  Instead, their workbench tops are
    overlaid with a conductive mat, which is itself wired to ground.
    
    So don't panic when you see the tech at ComputerCity playing with the
    guts of your machine sans wrist strap. 

re:                      <<< Note 951.6 by REGENT::POWERS >>>

>What do I do instead?  I ground myself or dissipate my charge by touching
>large hunks of metal on a regular basis, especially before I have to touch
>an isolated component, like a SIMM lying on a bench.

Are you saying that touching a large metal object that is NOT connected to the
earth will discharge your stored charge, and therefore make it safe for you to
then touch a sensitive device?  I thought you needed a path to earth to
discharge yourself (so the current has somewhere to go)?  On the other hand,
if we cause a shock by touching a doorknob (which is not connected to anything
but wood), I guess this proves your statement.  Maybe we only cause a shock
when we touch doorknobs on metal doors?

Is it the ability to store charge the most important thing, and NOT the
presence of a path to earth?  Are you saying that a large metal object can
store your charge (on its surface, if I remember my college physics),
therefore transferring the static electricity from you to the metal object?

thanks,

adam

    
    re:.7
    
    >I can see how a grounding strap would help when its connected to the
    >chassis of the machine and I reach in and remove a Simm...but I dont
    >see how it works when I then reach over and pick up that Simm lying on
    >the bench.
    
    I have (and even sometimes use) a static mat/wrist-strap/common-ground
    thingy. It's a conductive mat that you attach to the machine chassis
    and to your wrist. You place the SIMMs on the mat the machine on the
    mat (your left knee on the mat, your youngest child and any feline pets
    etc. on the mat) before you begin working. 
    
    I've never had a problem with zapped SIMMs using the mat and grounding
    straps...then again, I've done about 10 SIMM installs and a few NuBus
    card installs without any strap, just grabbing on to the power suppy
    and working that way and also never had a problem. The mat is very
    impressive to some people, others crack up. 
    
    Mario
    

>Are you saying that touching a large metal object that is NOT connected to the
>earth will discharge your stored charge, and therefore make it safe for you to
>then touch a sensitive device?  I thought you needed a path to earth to
>discharge yourself (so the current has somewhere to go)?  On the other hand,
>if we cause a shock by touching a doorknob (which is not connected to anything
>but wood), I guess this proves your statement.  Maybe we only cause a shock
>when we touch doorknobs on metal doors?

Actually, what is required to avoid damaging components is that your body's
electrical potential is MATCHED to the electrical potential of the object
that you are about to touch.  The wrist strap achieves that by providing a
conductive path between the two.  

The fact that a ground to Earth is not required is demonstrated by your 
doorknob example:  If you get a shock from a doorknob, and then immediately
reach out and touch it again, you will not get a second shock.  This is because
the potentials have been matched.

If the unit being serviced is not at ground potential, that will be resolved
via the grounding conductor when the unit is plugged in, with the current
passing through components capable of handling the power, rather than having
it pass from finger to sensitive semiconductors.

Kevin

    Re: .10
    
>    ... You place the SIMMs on the mat the machine on the mat (your left
>    knee on the mat, your youngest child and any feline pets etc. on the
>    mat) before you begin working.
>
>    ... The mat is very impressive to some people, others crack up.
    
    Are you sure you are not confusing the game board from "Twister" with a
    static grounding Mat?  Who spins the dial?
    
    					Bob Harris

    This from Kanata Manufacturing, where I worked as a Support
    Technologist for many years and have been a system manager for many
    years, etc... in other words, I have the knowledge and experience.
    
    We have a masssive investment in Conductive flooring and all employees
    working on any and all product wear conductive shoes. The employees
    test their shoes twice each day minimum and generally every time they
    are proceeding to the production floor. If the testing fails they are
    not allowed to work on product until the problem has been corrected. In
    addition to the shoes, all employees also wear blus smocks that contain
    thin wire threads throughout. These smocks are mandated to completely
    enclose the arms, thus covering up and shirt underneath. You are not
    allowed to roll up the sleeves and the smock must always be worn
    completely buttoned up. The smock, like a proper ESD bag is a faraday
    sheild.
    
    These shoes are only valid as long as the employee is standing up. The
    moment that an employee works in an area where they are required to sit
    down on the job, they must now also connect themselves up to a
    workstation ground, that is common to the ground on the floor,
    themselves and the workbench. The whole premise here is to equalize the
    static charge across everything and everyone.
    
    All modules are transported inside ESD bags, not on them, not wrapped
    in them but inside them.
    
    We allow the temporary use of heel straps on visitors and new
    employees, but heel straps have a valid lifetime of only 2 weeks, not
    good.
    
    The whole thing as described is born from scientific studies having
    been performed by our corporation in past years, mosr than 10 years
    ago. A specific DIGITAL standard covers this entire process and it's
    very regular and random auditing to ensure the systemn is followed and
    not being cheated.
    
    As an anecdote, we are one of the few manufacturers who actually take
    these very rigid procedures seriously. As a result, we are one of a
    very few manufacturers that do not experience premature failures
    induced by static discharge.
    
    Think about it folks, if we were to be blowing up every 2 Alpha chips
    in the manufacutring process, we'd have a heck of a Field Service
    expense on our hands.
    
    Always wear and follow thorough ESD procedures every time you are
    working on electronic equipment.
    
    By the way, all employees, Office Staff and Production Staff take
    mandatory ESD training every year.
    
    rtt