Grounding

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

John wrote:
My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)


The best way, is to use one of these. This is a disposable wrist strap.
On one end, is a shiny copper section, with an adhesive applied to a portion
of it. You stick that end, onto a shiny screw that bites into the chassis
metal somewhere. (I use a screw or rivet on the PSU.) The idea is, the copper
end of the wrist strap is at chassis potential. I've actually used the same
disposable wrist strap a number of times, so you don't have to throw it away
until it gets grubby.

(Order one when you buy memory...)
http://www.crucial.com/store/partspe...e=CTWRISTSTRAP

With the other end wrapped around your wrist, there is a high resistance
connection between you and the computer chassis. Perhaps somewhere around
1 megohm or so. The purpose of the high resistance, is to slowly drain
ESD off your body. (A fast discharge = high current flow, slow means a lower
magnitude current during equalization.) Then, pick up the ESD packaged DIMM,
open the package and install it.

If you don't have a strap, you can...

1) Put on a pair of summer shorts. This leaves bare legs.
2) Unplug computer, lay it in your lap. Remove the side panel, lay panel on the floor.
By the computer laying in your lap, part of the chassis touches bare skin,
bringing you to the same potential as the chassis. Touch shiny metal on
the chassis to be doubly sure.
3) Snip open DIMM package. Hold DIMM by edges (not the contacts). Finger
oils and salt are not good for the contacts. Insert DIMM
into slot. Check clips have snapped into the correct position.
4) Put the side panel back on. Plug in and test.
5) If DIMM is not detected, or programs like memtest86+ fail almost
immediately, you can...
6) Put the computer in your lap again. Make sure you are at the same potential
as the rest of the chassis. (Computer is unplugged, to ensure no +5VSB
is present.) Then, remove and reinsert the DIMM about five times. The removal
and insertion will help clean manufacturing dirt from the socket contacts.
The aqueous wash at the factory doesn't necessarily remove all debris. Avoid
the temptation to use other cleaning techniques. Removing precious gold from
contact surfaces is self defeating.
7) Put the side panel on again and retest.

A DIMM slot is powered (indirectly) via +5VSB. That is so, when a computer is
in sleep mode, the memory has power to help keep it refreshed. You don't want
to plug a DIMM into a slot which is electrified. Yes, you can flip off the
switch on the back of the computer, and *most* of the time there will be no
DC power inside the chassis. We've had one report here, where a cheap supply
continued to run, even when the switch was flipped to the off position (a
broken switch). Even though that is a remote possibility, unplugging the
computer guarantees there is no DC present inside the chassis. Wait at least
30 seconds after unplugging, before inserting the DIMM. My computer needs
about 30 seconds for all power to be drained by the standby loading. Then
it should be safe to work on a DIMM.

HTH,
Paul

"John" wrote in message
...
My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding
that she will be at the same potential as the case - but not necessarily
grounded to earth)


After seeing the way that memory strips are thrown into a box and rifled
through at computer shows I doubt there is anything worse that you could do.

Although I no longer bother to take precautions when working on my own
computers apart from turning off the power, it would be wrong of me to
advise you to do the same.

On Mon, 14 Jan 2008 11:19:16 GMT, "John"
wrote:

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)


The basic strategy is as follows:

1) Case should be connected to ground through the power
cord. (this is optional, but the easiest way when PSU has
an on/off switch).

2) User should be connected to ground through high
impedance (ESD strap or touching metal with serial megaohm
resistor connected to ground).

3) User should not be touching the system case when the
memory module is picked up, but should be electrically
connected through the ESD strap or megaohm resistor to
ground... to earth ground if the system is connected to
earth ground, or to system chassis ground if the system is
not connected to earth ground (like if the AC power cord has
to be unplugged because the PSU has no on/off switch).

There are three "bodies" here all possibly at a different
potential. Human, system, and memory module. Having the
system grounded to earth through the AC electrical system is
sufficient, so what remains is whether the memory module
itself is at same potential as the system, at ground
potential - but it is not enough to be touching the system
case because the case and memory module may not be at the
same potential yet. If earth ground through the AC outlet
is not possible, then connecting the ESD strap or megaohm
resistor to the system case serially and then touching the
memory will be sufficient.

What will not be safe is to have the case grounded, be
directly touching the case (with or without the ESD strap)
while picking up the memory module. So earth ground is not
important, but to slowly bring the memory module to the same
potential as the system ground is important. Earth ground
is just a very convenient reference.

Many people recommend that the PC be unplugged. This is primarily because when the PC is "switched off" there can still be power on the motherboard. It is better to leave the PC plugged in so that it is grounded and remove all power by turning off power at the power supply, power strip, or UPS.

John wrote:

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

--
Mike Walsh

John wrote:

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

Unplug the PC when installing ram, or any other card.







--
http://www.bootdisk.com/

On Jan 14, 11:19 am, "John" wrote:
My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

Read Plato! Anyone reading these replies would think the OP was
attempting to evade old Smokey (the electric chair) doing it's job, or
even HELP getting zapped. If anyone is SO unsure of how to go about
this op...LEAVE WELL ALONE! Get someone who knows to do it.

On Jan 14, 11:19 am, "John" wrote:
My daughter is about to replace a memory module. (UK based where we have
3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and
keep in contact with the case of the PC to remove static?

This is what I do. Just be sure that the PC is switch off at the BACK. If
your PSU doesn't have a power switch, then unplug it from the wall.

"John" wrote in message
...
My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding
that she will be at the same potential as the case - but not necessarily
grounded to earth)

Don't make much difference, but safest to switch it off and unplug.
Memeory modules are cheaper to replace than your daughter.
Then eart against the frame.
Don't forget to wear wellingtons,

John wrote:

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

The former is prohibited for safety reasons at the factories I've
visited.

The latter is safer and maybe even better for preventing damage, but
wear short sleeves to improve the likelihood that the forearms will be
in contact with the metal case, and to prevent static buildup on the
person, wear no shoes, socks, or stockings.

Google "ESD" (electrostatic discharge) for more information on proper
techniques.