Electrostatic Discharge-Esd Protection - Dell Latitude 5520 Service Manual

Once the system shuts down, you can perform the replacement procedures without disconnecting the battery cable from
the system board.
5. To exit Service Mode after finishing replacement procedures, connect AC adapter and press the power button to power on
the system. The system automatically returns to normal functioning mode.
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 For this reason, some previously approved methods of handling parts are no longer applicable.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.
10 Working inside your computer