Follow the safety precautions described in the following
sections when you perform an installation or a disassembly/reassembly
procedure.
Turn off the system and all attached peripherals.
Disconnect the system and all attached peripherals
from AC power.
Disconnect all network cables, telephone or telecommunications
lines from the system.
Use a wrist grounding strap and mat when working inside
any computer system to avoid electrostatic discharge (ESD) damage.
After removing a system component, carefully place
the removed component on an anti-static mat.
Wear shoes with non-conductive rubber soles to help
reduce the risk of being shocked or seriously injured in an electrical
accident.
Standby Power
Dell products
with standby power must be completely unplugged before the chassis
is opened. Systems that incorporate standby power are essentially
powered while turned off. The internal power enables the system to
be remotely turned on (wake on LAN), suspended into a sleep mode,
and have other advanced power management features.
After you unplug a system and before you remove components, wait
approximately 30 to 45 seconds to allow the charge to drain from the
circuits. Remove the battery from portable computers.
Bonding
Bonding is a method for connecting
two or more grounding conductors to the same electrical potential.
This is done through the use of a Field Service ESD kit. When connecting
a bonding wire, always ensure that it is connected to bare metal and
never to a painted or non-metal surface. The wrist strap should be
secure and in full contact with your skin, and be sure to always remove
all jewelry such as watches, bracelets, or rings.
Figure 1. Bonding
Electrostatic Discharge Protection
ESD is
a major concern when you handle electronic components, especially
sensitive components such as expansion cards, processors, memory DIMMs,
and system boards. Very slight charges can damage circuits in ways
that may not be obvious, such as intermittent problems or a shortened
product life span. As the industry pushes for lower power requirements
and increased density, ESD protection is an increasing concern.
Due to the increased density of semiconductors used
in recent Dell products, the sensitivity to static damage is now higher
than in earlier Dell products. For this reason, some previously approved
methods of handling parts are no longer applicable.
There are two recognized types of ESD damage: catastrophic and intermittent
failures.
Catastrophic —The damage causes an immediate
and complete loss of device functionality. An example of catastrophic
failure is a memory DIMM that has received a static shock and immediately
generates a "No POST/No Video" symptom with a beep code emitted for
missing or nonfunctional memory.
NOTE: Catastrophic failures
represent approximately 20 percent of ESD-related failures.
Intermittent —The DIMM receives a static shock,
but the tracing is merely weakened and does not immediately produce
outward symptoms related to the damage. The weakened trace may take
weeks or months to melt, and in the meantime may cause degradation
of memory integrity, intermittent memory errors, etc.
NOTE: Intermittent failures
represent approximately 80 percent of ESD-related failures. The high
rate of intermittent failures means that most of the time when damage
occurs, it is not immediately recognizable.
The more difficult type of damage to recognize
and troubleshoot is the intermittent (also called latent or “walking
wounded”) failure. The following image shows an example of intermittent
damage to a memory DIMM trace. Although the damage is done, the symptoms
may not become an issue or may not cause permanent failure symptoms
for some time after the damage occurs.
Figure 2. Intermittent
Do the following to prevent ESD damage:
Use a wired ESD wrist strap that is properly grounded.
The use of wireless anti-static straps is no longer allowed;
they do not provide adequate protection.
Touching
the chassis before handling the parts does not ensure adequate ESD
protection on parts with increased sensitivity to ESD damage.
Figure 3. Chassis Bare
Metal grounding (unacceptable)
Handle all static-sensitive components in a static-safe
area. If possible, use anti-static floor pads and workbench pads.
When handling static-sensitive components, grasp them
by the sides, not by the top. Avoid touching pins and circuit boards.
When unpacking a static-sensitive component from
its shipping carton, do not remove the component from the anti-static
packing material until you are ready to install the component. Before
unwrapping the anti-static packaging, be sure to discharge static
electricity from your body.
Before transporting a static-sensitive component,
place it in an anti-static container or packaging.
The ESD field service kit
The unmonitored Field Service kit is the most commonly used. Each
Field Service kit includes three main components: anti-static mat,
wrist strap, and bonding wire.Figure 4. ESD field service
kit
The anti-static mat is dissipative and should be used
to safely place parts on during service procedures. When using an
anti-static mat, your wrist strap should be snug and the bonding wire
should be connected to the mat and to bare-metal on the system being
worked on. Once deployed properly, service parts can be removed from
the ESD bag and placed directly on the mat. Remember, the only safe
place for ESD-sensitive items are in your hand, on the ESD mat, in
the system, or inside a bag.Figure 4. Anti-static
mat
The wrist strap and bonding wire can be either directly
connected between your wrist and bare metal on the hardware if the
ESD mat is not required, or connected to the anti-static mat to protect
hardware that is temporarily placed on the mat. The physical connection
of the wrist strap and bonding wire between your skin, the ESD mat,
and the hardware is known as bonding. Use only Field Service kits
with a wrist strap, mat, and bonding wire. Never use wireless wrist
straps.
Always be aware that the internal wires of a wrist
strap are prone to damage from normal wear and tear, and must be checked
regularly with a wrist strap tester in order to avoid accidental ESD
hardware damage. It is recommended to test the wrist strap and bonding
wire a minimum of once per week.
Table 1. Wrist strapsThe following shows a wrist strap and bonding wire
and a wireless ESD strap.
Wrist strap and bonding wire
Wireless ESD Strap (unacceptable)
Figure 6. Wrist strap
and bonding wire
Figure 7. Wireless ESD
strap (unacceptable)
ESD Wrist Strap Tester
The wires inside of an ESD strap are prone to damage over time. When
using an unmonitored kit, it is best practice to regularly test the
strap prior to each service call, and at a minimum, test once per
week. A wrist strap tester is the best method for doing this test.
If you do not have your own wrist strap tester, check with your regional
office to find out if they have one. To perform the test, plug the
wrist-strap’s bonding-wire into the tester while it is strapped to
your wrist and push the button to test. A green LED is lit if the
test is successful; a red LED is lit and an alarm sounds if the test
fails.Figure 8. ESD wrist strap
tester
Insulator elements
It is critical
to keep ESD sensitive devices, such as plastic heat sink casings,
away from internal parts that are insulators and often highly charged.
Table 2. Placement of
Insulator ElementsThe following shows unacceptable and acceptable
placement for insulator parts relative to ESD sensitive devices.
Unacceptable
Acceptable
Figure 9. Unacceptable
— DIMM lying on an insulator part (plastic heat sink shroud)
Figure 10. Acceptable —
DIMM separated from the insulator part
Consider the working environment
Before deploying the ESD Field Service kit, assess
the situation at the customer location. For example, deploying the
kit for a server environment is different than for a desktop or portable
environment. Servers are typically installed in a rack within a data
center; desktops or portables are typically placed on office desks
or cubicles.
Always look for a large open flat
work area that is free of clutter and large enough to deploy the ESD
kit with additional space to accommodate the type of system that is
being repaired. The workspace should also be free of insulators that
can cause an ESD event. On the work area, insulators such as Styrofoam
and other plastics should always be moved at least 12 inches or 30
centimeters away from sensitive parts before physically handling any
hardware components.
ESD packaging
All ESD-sensitive devices must be shipped and received
in static-safe packaging. Metal, static-shielded bags are preferred.
However, you should always return the damaged part using the same
ESD bag and packaging that the new part arrived in. The ESD bag should
be folded over and taped shut and all the same foam packing material
should be used in the original box that the new part arrived in.
ESD-sensitive devices should be removed from packaging
only at an ESD-protected work surface, and parts should never be placed
on top of the ESD bag because only the inside of the bag is shielded.
Always place parts in your hand, on the ESD mat, in the system, or
inside an anti-static bag.Figure 11. ESD packaging
Transporting sensitive components
When transporting
ESD-sensitive components such as replacement parts or parts to be
returned to Dell, it is critical to place these parts in anti-static
bags for safe transport.
ESD protection summary
It is strongly suggested that all field service
engineers use the traditional wired ESD grounding wrist strap and
protective anti-static mat at all times when servicing Dell products.
In addition, it is critical that engineers keep sensitive parts separate
from all insulator parts while performing service and that they use
anti-static bags for transporting sensitive components.
Lifting equipment
NOTE: Do not lift greater than 50 pounds. Always obtain assistance
from another person or persons, or use a mechanical lifting device.
Adhere to the following guidelines when lifting equipment:
Get a firm balanced footing. Keep your feet apart
for a stable base, and point your toes out.
Bend your knees. Do not bend at the waist.
Tighten stomach muscles. Abdominal muscles support
your spine when you lift, offsetting the force of the load.
Lift with your legs, not your back.
Keep the load close. The closer it is to your spine,
the less force it exerts on your back.
Keep your back upright, whether lifting or setting
down the load. Do not add the weight of your body to the load. Avoid
twisting your body and back.
Follow the same techniques in reverse to set the
load down.
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