rb wrote:
> PcGAmeR22;1341926 Wrote:
>> A friend of mine bought a new graphics card for his computer and he also
>> got a high end power supply , I told him to contact me when possible so
>> i can go to his place and install the new upgrades
>> I dont wanna end up messing it up he is low on budget so i would like to
>> know
>> whats the best way to discharge static electricty before opening the
>> case and working in it
>
> Use an ESD Wrist Strap such as-->
> http://www.radioshack.com/product/in...ductId=2103245
>
> Or at the very least touch the case frame inside (unpainted metal) from
> time to time while working with the PC.
> Remember to avoid touching chips, contacts or pins when handling or
> installing cpu, memory sticks, and expansion cards...always hold or
> press from the edges.
The desired function, is to "bring all components to a common electrostatic
potential before assembly".
That means occasionally touching the chassis, doesn't count. Once you
remove your grasp from the chassis, now the items are "charging up again".
http://en.wikipedia.org/wiki/Electrostatic_discharge
tribocharging, electrostatic induction
Even electrolytic capacitors will do that, but for different reasons. If
you take a shorting strap and discharge an electrolytic, then release the
strap, the capacitor will still have residual charge. In fact, on the old
high voltage caps, there is still a significant shock hazard if you
do it that way.
So the purpose of the ESD wrist strap, is you connect it to the chassis,
and connect it to you. The wrist strap should have around a 1 megohm
resistor in series with it. The charge on you and the chassis equalize
slowly and the potential difference is zero.
While holding the ESD bag the video card came in, you touch and hold
the inside of the bag, while at the same time withdrawing the card
from the bag. Now, you hold the faceplate of the card (as it is grounded),
and try to continuously hold that while inserting the card. The chassis
and you are at a common potential because of the wrist strap, but the
video card would only be at the same potential, for as long as you're
touching the faceplate. You may need to switch hands while inserting
the card, to maintain continuous contact.
One reason for this degree of care, is some Nvidia motherboard chipsets
in the past, ended up with "blown out" PCI Express slots. Which suggests
the electrical signals in the slot on the motherboard, are overly sensitive
to static.
Using an ESD strap, plus using some care while inserting the video
card, should lead to a successful install. You can "simulate" the
common potential thing by cheating, but it's pretty hard to maintain
contact until the install is finished.
Devices vary, in their ability to resist ESD. I've worked with MOSFETs
in a transistor can (four legs), where there are no clamp diodes, and
the device has a 30V ESD rating. ICs can have 1001 volts, 2001 volts or higher
ratings. Those are relatively robust, compared to the 30 volt parts.
USB ports are around 5-6kV of ESD rating. The very best parts, are
RS232 chips with 15kV ESD rating on the modem data pin end. RS232
chips needed those ratings, because of the large numbers of RS232
chips blown out by static. I replaced a bunch while I was working,
on things like test equipment and even on the computers we built.
(MC1488, MC1489 chips). With the newer 15kV rating, doing replacements
like that is a thing of the past.
A human can build up a reasonable level of ESD charge, to the 50kV
level. That means if you're completely clueless, scuff across
the carpet and then touch the PCI Express slot on your motherboard,
it's going to be blown. Even the RS232 chips could be blown, if you
could get close enough to the pins while scuffing across the carpet.
A lot of connectors, due to the metal shell around the pins, that
provides "direct contact protection", where the discharge would
have gone right into the pin. But ESD can also do damage by induction,
which is how a lot of stuff in your house gets damaged in a
lightning storm. A conductor could be hit 100 feet from you,
and just the induced voltage in conductors within the house,
will destroy stuff. The same is true of ESD discharge on connectors,
in that, the charge may dissipate into the chassis, but not before
being induced into adjacent conductors.
This is one of the proposed failure mechanisms on ICH5. A user discharges
ESD into the metal shell of the front panel USB connector. But because
the metal shell doesn't have a good connection to metal in the chassis
(the front panel is typically made of plastic), the discharge into ground
goes down the ground wire in the USB front panel cable. But at the
same time, the ESD is induced into the adjacent D+ and D- signals,
leading to latchup failure at the ICH5. So in the computer, one of
the worst designs from an ESD defense point of view, is front
panel connectors. By seating the connectors in plastic, that's asking for
induction based failures. And is why I recommend making connections
to a PC, via the rear connectors. As everything back there has a
metal connection to the chassis. That's why the rear I/O plate
has those "springy fingers". It helps with ESD. The springy fingers
shorten the distance an ESD charge has to travel, to get to the chassis
metal.
Paul
Avoiding Static electricty 
Linear Mode
