Safety Precautions; Electrostatic Discharge-Esd Protection - Dell Latitude 7220 Service Manual

NOTE: To avoid electrostatic discharge, ground yourself by using a wrist grounding strap or by periodically touching
an unpainted metal surface simultaneously as touching a connector on the back of the tablet.
7. Remove any installed ExpressCards or Smart Cards from the appropriate slots.

Safety precautions

The safety precautions chapter details the primary steps to be taken before performing any disassembly instructions.
Observe the following safety precautions before you perform any installation or break/fix procedures involving disassembly or reassembly:
• Turn off the tablet and all attached peripherals.
• Disconnect the tablet and all attached peripherals from AC power.
• Disconnect all network cables, telephone, and telecommunications lines from the system.
• Use an ESD field service kit when working inside any tablet to avoid electrostatic discharge (ESD) damage.
• After removing any system component, carefully place the removed component on an antistatic mat.
• Wear shoes with nonconductive rubber soles to reduce the chance of getting electrocuted.
Bonding
Bonding is a method for connecting two or more grounding conductors to the same electrical potential. This is done by using a field
service electrostatic discharge (ESD) kit. When connecting a bonding wire, ensure that it is connected to bare metal and never to a
painted or nonmetal surface. The wrist strap should be secure and in full contact with your skin, and ensure that you remove all jewelry
such as watches, bracelets, or rings prior to bonding yourself and the equipment.
Electrostatic discharge—ESD 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
previous Dell products. For this reason, some previously approved methods of handling parts are no longer applicable.
Two recognized types of ESD damage are catastrophic and intermittent failures.
• Catastrophic – Catastrophic failures represent approximately 20 percent of ESD-related failures. 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.
• Intermittent – 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 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.
The more difficult type of damage to recognize and troubleshoot is the intermittent (also called latent or "walking wounded") failure.
Perform the following steps 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 parts does not ensure adequate ESD protection on parts with increased
sensitivity to ESD damage.
• Handle all static-sensitive components in a static-safe area. If possible, use anti-static floor pads and workbench pads.
• 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, ensure that you discharge static
electricity from your body.
• Before transporting a static-sensitive component, place it in an anti-static container or packaging.
Working on your tablet 7