Dell Vostro 3681, Service Manual

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CAUTION: To disconnect a network cable, first unplug the cable from your computer and then unplug the cable from
the network device.
5. Disconnect your computer and all attached devices from their electrical outlets.
6. Press and hold the power button while the computer is unplugged to ground the system board.
NOTE: To avoid electrostatic discharge, ground yourself by using a wrist grounding strap or by periodically touching
an unpainted metal surface at the same time as touching a connector on the back of the computer.
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 system and all attached peripherals.
• Disconnect the system 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 tabletnotebookdesktop to avoid electrostatic discharge (ESD) damage.
• After removing any system component, carefully place the removed component on an anti-static mat.
• Wear shoes with non-conductive rubber soles to reduce the chance of getting electrocuted.
Standby power
Dell products with standby power must be unplugged before you open the case. 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) and suspended into a sleep
mode and has other advanced power management features.
Unplugging, pressing and holding the power button for 15 seconds should discharge residual power in the system board.
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 electrostatic discharge (ESD) kit. When connecting a bonding wire, 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 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.
6 Working on your computer