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anti-static/grounding question...

 
 
Richard
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      01-03-2006
Mark Robinson wrote:

> If you earth yourself to the case of the machine with a grounding strap,
> you still need to consider how you handle components you are installing
> into the machine. Touching something that's not earthed when you are
> doesn't protect that thing from static electricity that it may be
> carrying and which may discharge through you to earth. That's why
> commercial antistatic workstations include a mat for the work surface.


Which is why the sealed antistatic bag should be placed on the static
worksurface, and opened on it and then the contents placed on it. The bag will
charge/discharge the contents uniformly and safely to the potential of the
worksurface.

The static work surface should be at the same potential as the computer that you
are also working on, this doesnt have to be the ground ground, but its usual
that it is since the computers going to be plugged in at some stage.
 
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XP
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      01-03-2006
On Tue, 03 Jan 2006 10:25:09 GMT, Stephen Worthington
<(E-Mail Removed)34.nz56.remove_numbers> wrote:

>On Tue, 03 Jan 2006 20:42:04 +1300, gimp <(E-Mail Removed)> wrote:
>
>>every motherboard manual i've read says when doing a system build the
>>power cable should be unplugged to avoid electric shock.... but
>>seriously if its switched off at the wall there's no danger - is that
>>correct...? also does touching the PSU still work as a ground if the
>>cable is unplugged..?

>
>I always work on my PC with the mains cable in, but the wall switch
>off, in order to retain an earth connection. If it is not plugged in,
>then there will be no earth. I always use a DSE earthing strap - it
>is much safer than trying to remember to ground yourself at crucial
>times. I consider it pretty safe to work like this as long as I am
>not trying to work on the inside of the power supply - when you open
>the power supply case, you are exposing high voltage wiring and
>*really* need the assurance of unplugging from the wall.
>
>The voltages on the outside of the power supply are not at all
>dangerous to a human, as long as the power supply has not suffered a
>catastrophic fault that allows the high voltages through it into the
>PC, so your real danger if someone turns the power on is firstly that
>you will damage your PC and secondly that the fans will catch a bit of
>you or your clothing.
>
>If you are leaving the plug in, make sure that where you are working
>on the PC has the plug in your field of view, so no-one can turn it on
>again without you noticing. If you can not do that, put parcel tape
>over the switch and label it with a marker pen: "DO NOT TURN ON!" and
>your name.





YOU DO NOT NEED A EARTH CONNECTION WHEN WORKING ON A PC AND MOBO, YOU JUST
NEED A ANTI STATIC STRAP.


ITS THE POTENAL DIFFERENCE BETWEEN YOU AND THE COMPUTER CASE THAT MATTERS..


 
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XP
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      01-03-2006
On Wed, 04 Jan 2006 00:02:15 +1300, Mark Robinson <(E-Mail Removed)2tod.net>
wrote:

>gimp wrote:
>> every motherboard manual i've read says when doing a system build the
>> power cable should be unplugged to avoid electric shock.... but
>> seriously if its switched off at the wall there's no danger - is that
>> correct...? also does touching the PSU still work as a ground if the
>> cable is unplugged..?

>
>I don't see any advantage in grounding the machine to mains earth while
>building a system, in fact this will improve the chances of damage from static
>electricity as the path to ground for the static will be improved.
>
>In the absence of a grounding strap keeping skin touching a metallic part of
>the case is better than nothing but the closer you get to an antistatic
>workstation the fewer random deaths you will suffer.
>
>The idea is to keep you, the machine and all the components you are putting
>into it close to the same voltage.
>
>If you earth yourself to the case of the machine with a grounding strap, you
>still need to consider how you handle components you are installing into the
>machine. Touching something that's not earthed when you are doesn't protect
>that thing from static electricity that it may be carrying and which may
>discharge through you to earth. That's why commercial antistatic workstations
>include a mat for the work surface.






Totally correct..


 
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XP
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      01-03-2006
On Wed, 04 Jan 2006 00:19:03 +1300, Richard <(E-Mail Removed)> wrote:

>Mark Robinson wrote:
>
>> If you earth yourself to the case of the machine with a grounding strap,
>> you still need to consider how you handle components you are installing
>> into the machine. Touching something that's not earthed when you are
>> doesn't protect that thing from static electricity that it may be
>> carrying and which may discharge through you to earth. That's why
>> commercial antistatic workstations include a mat for the work surface.

>
>Which is why the sealed antistatic bag should be placed on the static
>worksurface, and opened on it and then the contents placed on it. The bag will
>charge/discharge the contents uniformly and safely to the potential of the
>worksurface.
>
>The static work surface should be at the same potential as the computer that you
>are also working on, this doesnt have to be the ground ground, but its usual
>that it is since the computers going to be plugged in at some stage.




The biggest problem with putting in a MoBo is shorting the CMOS battery to
other logic parts, the 3v battery can blow up IC's


Is far better to remove it and wait a few minuets for the CMOS circuit to
discharge its self.


 
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Stephen Worthington
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      01-03-2006
On Wed, 04 Jan 2006 00:19:03 +1300, Richard <(E-Mail Removed)> wrote:

>Mark Robinson wrote:
>
>> If you earth yourself to the case of the machine with a grounding strap,
>> you still need to consider how you handle components you are installing
>> into the machine. Touching something that's not earthed when you are
>> doesn't protect that thing from static electricity that it may be
>> carrying and which may discharge through you to earth. That's why
>> commercial antistatic workstations include a mat for the work surface.

>
>Which is why the sealed antistatic bag should be placed on the static
>worksurface, and opened on it and then the contents placed on it. The bag will
>charge/discharge the contents uniformly and safely to the potential of the
>worksurface.
>
>The static work surface should be at the same potential as the computer that you
>are also working on, this doesnt have to be the ground ground, but its usual
>that it is since the computers going to be plugged in at some stage.


If you do not have a static mat, the next best thing is to put the
gear down in its bag on the metal PC chassis so it can ground itself.
Give it a couple of seconds, then, wearing your grounding strap
connected to the PC chassis, you can safely pick it up again and open
the bag to install what is inside. I like the way my server case
works for this - it has bare metal at the top when upright with the
covers off, great for putting things down on. My workstation case has
a painted top when I have the side covers off - not a good earth - so
I normally lay it down on its side to work on it so I don't forget and
put things on the top.
 
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Don Hills
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      01-03-2006

In article <(E-Mail Removed)2tod.net>,
Mark Robinson <(E-Mail Removed)2tod.net> wrote:

.... the best advice given so far in this thread. I won't requote it, but I
will summarise it. This is relevant to home workers, I would hope someone
doing it for a living would have all the right kit and would know how to use
it.

Unplug the mains lead from the wall. No exceptions. Most modern PCs have 5
volts present on the motherboard even when powered off - this is to run the
"wake on LAN, wake on ring, wake on alarm" functions. It's not always the
case, but making no exceptions ensures no problems. The 5 volts isn't
dangerous to you, but shorting it out may damage the motherboard.

Do not get hung up on trying to keep the PC at earth potential while working
on it. What is important is to keep the PC, you, and all parts being changed
at the same potential and, hopefully, close to earth potential.

An anti-static strap is a good idea for those who have not learned to keep
one hand (or arm, or wrist etc) on the chassis at all times. The machine
itself usually provides a sufficiently large work area for placing parts
being removed or replaced. Lay tower machines on their side. If you need
more room, a sheet of tinfoil laid with one end under the machine in contact
with bare metal will work fine. Obviously a true antistatic work mat would
be ideal but they aren't cheap and for some reason there's never one around
when you need one.

Never open an antistatic bag unless it is lying on the machine or antistatic
work surface. If you pick it up to open it, hold it back down on the machine
as you withdraw the part. Never place unprotected parts down anywhere other
than on the machine or work surface until they have been rebagged.

If you have to leave the machine and come back, reattach your antistatic
strap or touch the metal frame well away from any loose parts before
continuing. If you're working in a bad environment where simply walking
across the carpet causes you to draw sparks from door handles etc, find
something handy to touch that will discharge you before touching the machine
such as a water tap, concrete floor, metal window frame etc.

--
Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
"New interface closely resembles Presentation Manager,
preparing you for the wonders of OS/2!"
-- Advertisement on the box for Microsoft Windows 2.11 for 286
 
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Bruce Knox
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      01-03-2006
On Wed, 4 Jan 2006 00:11:09 +1300, Rob J <(E-Mail Removed)> wrote:

....
>> source. Likewise it does not matter if the earth is above true earth.
>> You are trying to minimise voltage differentials. If the case is at 30
>> volts then everything should be at 30 volts.

>
>If you touch this and something that is at true earth you get zapped.

Which you would just by touching the case. No need to open it up. Does
not happen very often as if the electrical earth is elevated then the
whole area is. Specially in a house built since full electrical earth
bonding has been a requirement.
>
>> On all pcs I have seen unless you are working on the power supply (a
>> sealed system) there is no way of contacting dangerous voltages.

>
>Only true of ATX and later designs.
>
>Earlier PCs often had a front panel 230V power switch with mains wiring
>between it and the power supply.

True. I forgot about the bad old days. In theory you need at least an
electrical service technicians certificate to even open one of those
cases (if it is your job).

Bruce http://www.baggins.co.nz
http://physio.otago.ac.nz
 
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gimp
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      01-03-2006
Don Hills wrote:
> Unplug the mains lead from the wall. No exceptions. Most modern PCs have 5
> volts present on the motherboard even when powered off - this is to run the
> "wake on LAN, wake on ring, wake on alarm" functions.



i've used the wake-on functions before but IME they only work when the
PSU is at on (i don't mean the pc switched on, i mean the lil' on/off
switch at the back of the PSU), and the power is on at the wall.

i've had no problems when grounding with the case but i think i will get
an anti-static strap to make life easier
 
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whoisthis
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      01-03-2006
In article <dpd9mk$836$(E-Mail Removed)>, gimp <(E-Mail Removed)>
wrote:

> every motherboard manual i've read says when doing a system build the
> power cable should be unplugged to avoid electric shock.... but
> seriously if its switched off at the wall there's no danger - is that
> correct...? also does touching the PSU still work as a ground if the
> cable is unplugged..?


So far all I have read is bullshit from everyone else.

Fact: Your body can build up a static charge of tens of thousands of
volts, and higher. The fact that this is a static charge means that
there is little energy (joules) involved so you will not kill yourself
with this charge, but it can make someone jump when you touch them.

Fact: When you body has a high static charge you do not even need to
touch some components for damage to be done. There is "soft" damage
which will not instantly kill a component, but will cause it to fail
1-12 months later. Want proof of this, then think back to when you were
a kid and remember how you could pick up bits of paper with a comb after
brushing your hair.

Fact: The semiconductors are now being built with much smaller
dimensions, down to 65nm. Human hair diameters range from 40 microns to
120 microns, ie about 1,000 time greater. 1nm is 1 billionth of a meter.
This means that a voltage of 65v as an equivalent volts/meter of 1
MILLION volts/meter. If you have a static charge of 65,000 volts that
would have the equivalent volts per meter of 65 BILLION volts per meter.
now then Voltage in a cloud-to-ground strike is 100 million to 1 billion
volts.

Fact: A proper earth strap should have an integrated resistor built into
it, this is FAR safer than just touching the case. Last thing you want
is to accidentally be earthed via zero ohms and touch something
connected to the mains.

Fact : You should work off an earthing mat too. Some places even have
special antistatic flooring too.

Fact : Too many "pc service people" do NOT take adequate protections,
there are some companies that I would NEVER take anything to because
they are lax with precautions.



go here to read more

http://www.semiconductors.philips.co...ous/IC26_CHAPT
ER_3_2000.pdf

and here
http://assets.zarlink.com/AN/esd3.pdf

and here

http://www.marktechopto.com/pdfs/ESDPrecautions.PDF
 
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~misfit~
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      01-03-2006
gimp wrote:
> Don Hills wrote:
>> Unplug the mains lead from the wall. No exceptions. Most modern PCs
>> have 5 volts present on the motherboard even when powered off - this
>> is to run the "wake on LAN, wake on ring, wake on alarm" functions.

>
>
> i've used the wake-on functions before but IME they only work when the
> PSU is at on (i don't mean the pc switched on, i mean the lil' on/off
> switch at the back of the PSU), and the power is on at the wall.
>
> i've had no problems when grounding with the case but i think i will
> get an anti-static strap to make life easier


Yeah, not all PSUs have an on/off switch.
--
~misfit~


 
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