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Removal and Replacement
This chapter provides
general service information for Compaq Presario 3500 Series Personal Computers. Adherence
to the procedures and precautions described in this chapter is essential for proper
service.
The topics discussed in
this section include the following:
A sudden discharge of
static electricity from a finger or other conductor can destroy static-sensitive devices
or microcircuitry. Often the spark is neither felt nor heard, but damage occurs. An
electronic device exposed to electrostatic discharge (ESD) may not be affected at all and
will work perfectly throughout a normal cycle. Or it may function normally for a while,
then degrade in the internal layers, reducing its life expectancy.
Networks built into many
integrated circuits provide some protection, but in many cases, the discharge contains
enough power to alter device parameters or melt silicon junctions.
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The accompanying table
shows typical electrostatic voltages generated by different activities.
Typical Electrostatic Voltages |
¡@ |
Relative
Humidity |
Event |
10% |
40% |
55% |
Walking across
carpet |
35,000 V |
15,000 V |
7,500 V |
Walking across
vinyl floor |
12,000 V |
5,000 V |
3,000 V |
Motions of
bench worker |
6,000 V |
800 V |
400 V |
Removing DIPS
from plastic tubes |
2,000 V |
700 V |
400 V |
Removing DIPS
from vinyl trays |
11,500 V |
4,000 V |
2,000 V |
Removing DIPS
from Styrofoam |
14,500 V |
5,000 V |
3,500 V |
Removing
bubble pack from PCBs |
26,000 V |
20,000 V |
7,000 V |
Packing PCBs
in foam-lined box |
21,000 V |
11,000 V |
5,000 V |
NOTE: 700
volts can degrade a product. |
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Many electronic components
are sensitive to ESD. Circuitry design and structure determine the degree of sensitivity.
The following proper packaging and grounding precautions are necessary to prevent damage:
- Protect all electrostatic parts and
assemblies with conductive or approved containers or packaging.
- Keep electrostatic sensitive parts in
their containers until they arrive at static-free stations.
- Place items on a grounded surface before
removing them from their
container.
- Always be properly grounded when touching
a sensitive component or assembly.
- Place reusable electronic-sensitive parts
from assemblies in protective packaging or conductive foam.
- Use transporters and conveyors made of
antistatic belts and metal roller bushings. Mechanized equipment used for moving materials
must be wired to ground and proper materials selected to avoid static charging. When
grounding is not possible, use an ionizer to dissipate electric charges.
The accompanying table
shows typical static-shielding protection levels afforded by different protective
packaging materials.
Static-Shielding Protection Levels |
Method |
Voltages |
Antistatic
Plastic |
1,500 |
Carbon-Loaded
Plastic |
7,500 |
Metallized
Laminate |
15,000 |
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To prevent static damage to
hard drives, use the following precautions:
- Handle drives gently, using
static-guarding techniques.
- Store drives in the original shipping
containers.
- Avoid dropping drives from any height
onto any surface.
- Handle drives on surfaces that have at
least one inch of shock-proof foam.
- Always place drives PCB assembly side
down on the foam.
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The method for grounding
must include a wrist strap or a foot strap at a grounded workstation. When seated, wear a
wrist strap connected to a grounded system. When standing, use footstraps and a grounded
floor mat.
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Grounding Workstations
To prevent static damage at
the workstation, use the following precautions:
- Cover the workstation with approved
static-dissipative material.
- Provide a wrist strap connected to the
work surface and properly grounded tools and equipment.
- Use static-dissipative mats, heel straps,
or air ionizers to give added protection.
- Handle electrostatic sensitive
components, parts, and assemblies by the case or PCB laminate. Handle them only at
static-free workstations.
- Avoid contact with pins, leads, or
circuitry.
- Turn off power and input signals before
inserting and removing connectors or test equipment.
- Use fixtures made of static-safe
materials when fixtures must directly contact dissipative surfaces.
- Keep work area free of nonconductive
materials such as ordinary plastic assembly aids and Styrofoam.
- Use field service tools, such as cutters,
screwdrivers, vacuums, that are conductive.
- Use a portable field service kit with a
static dissipative vinyl pouch that folds out of a work mat. Also use a wrist strap and a
ground cord for the work surface. Ground the cord to the chassis of the equipment
undergoing test or repair.
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Use the following equipment
to prevent static electricity damage to the equipment:
- Wrist Straps are flexible straps with a minimum of 1 mega ohm +/- 10% resistance to the ground cords. To provide proper ground, a
strap must be worn snug against the skin. On grounded mats without banana-plug connectors,
connect a wrist strap with alligator clips.
- Heelstraps/Toestraps/Bootstraps can be used at standing
workstations and are compatible with most types of boots and shoes. On conductive floors
or dissipative floor mats, use them on both feet with a minimum of 1 mega ohm resistance between operator and ground. To be effective, the
conductive strips must be worn in contact
with the skin.
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Other materials and
equipment that are recommended for use in preventing static electricity include:
- Antistatic tape
- Antistatic smocks, aprons, or sleeve
protectors
- Conductive bins, and other assembly or
soldering aids
- Conductive foam
- Conductive tabletop workstations with ground cord of 1 mega ohm
of resistance
- Static dissipative table or floor mats
with hard tie to ground
- Field service kits
- Static awareness labels
- Wrist straps and footwear straps providing 1 mega ohm (+/- 10%) resistance
- Material handling packages
- Conductive plastic bags
- Conductive plastic tubes
- Conductive tote boxes
- Metal tote boxes
- Opaque shielding bags
- Transparent metallized shielding bags
- Transparent shielding tubes
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- Torx T-8, T-10, and T-15 screwdrivers
(included in kit number 130619-001)
- Needle-nose pliers
- Flat-bladed screwdriver
- Diagnostics software
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The screws used in these
products are not interchangeable. If an incorrect screw is used during the reassembly
process, it could cause damage to the unit. Compaq strongly recommends that all screws
removed during the disassembly process be kept with the part that was removed, then
returned to their proper locations.
IMPORTANT: |
As each subassembly is removed from the computer, it should be placed
away from the work area to prevent damage |
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Most cables used throughout
the unit are ribbon cables. These cables must be handled with extreme care to avoid
damage.
Apply only the tension
required to seat or unseat the cables during insertion or removal from the connector.
Handle cables by the connector whenever possible. In all cases, avoid bending, twisting,
or tearing the cables, and ensure that cables are placed in such a way that they cannot be
caught or snagged by parts being removed or replaced.

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CAUTION: When servicing these computers, ensure that cables
are placed in their proper location during the reassembly process. Improper cable
placement can cause severe damage to the unit. |
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