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chapter
4
CAUTION: When the computer is plugged into an AC power source, there is always voltage applied to the system board. You must disconnect the power cord from the power source before opening the computer to prevent system board or component damage.
REMOVAL & REPLACEMENT PRELIMINARIES
This chapter provides general service information for the computer. Adherence to the procedures and precautions described in this chapter is essential for proper service.
4.1
Electrostatic Discharge Information
A sudden discharge of static electricity from your finger or other conductor can destroy staticsensitive 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 can work perfectly throughout a normal cycle. The device 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.
4.1.1
Generating Electrostatic Voltage
The following table shows that:
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Different activities generate different amounts of electrostatic voltage (static electricity). Electrostatic voltage increases as humidity decreases.
Activity
700 volts can degrade a product.
Relative Humidity 55%
7,500 V 3,000 V 400 V 400 V 2,000 V 3,500 V
40%
15,000 V 5,000 V 800 V 700 V 4,000 V 5,000 V
10%
35,000 V 12,000 V 6,000 V 2,000 V 11,500 V 14,500 V
Walking across carpet Walking across vinyl floor Motions of bench worker Removing DIPs* from plastic tube Removing DIPs* from vinyl tray Removing DIPs* from Styrofoam
Removing bubble pack from PCB 7,000 V 20,000 V 26,500 V Packing PCBs in foam-lined box 5,000 V 11,000 V 21,000 V *Dual Inline Packaging (DIP) is the packaging around individual microcircuitry. These are then multi-packaged inside plastic tubes, trays, or Styrofoam.
Compaq Deskpro EN Series of Personal Computers
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4.1.2
Preventing Electrostatic Damage to Equipment
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 to electric components and accessories.
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To avoid hand contact, transport products in static-safe containers such as tubes, bags, or boxes. 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. Avoid contact with pins, leads, or circuitry. Place reusable electrostatic-sensitive parts from assemblies in protective packaging or conductive foam.
4.1.3
Personal Grounding Methods and Equipment
Use the following equipment to prevent electrostatic damage to equipment: Wrist straps are flexible straps with a minimum of one-megohm +/- 10% resistance in the ground cords. To provide proper ground, a strap must be worn snug against bare skin. The ground cord must be connected and fit snugly into the banana plug connector on the grounding mat or workstation. Heel straps/Toe straps/Boot straps can be used at standing workstations and are compatible with most types of shoes or boots. On conductive floors or dissipative floor mats, use them on both feet with a minimum of one-megohm +/- 10% resistance between the operator and ground.
Static Shielding Protection Levels
Method
Antistatic plastic Carbon-loaded plastic Metallized laminate
Voltage
1,500 7,500 15,000
4.1.4
Grounding the Workstation
To prevent static damage at the workstation, use the following precautions:
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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, foot 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. Turn off power and input signals before inserting and removing connectors or test equipment.
4-2
Removal & Replacement Preliminaries
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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, and vacuums, that are conductive.
4.1.5
Recommended Materials and Equipment
The following materials and equipment are recommended for use in preventing static electricity include:
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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 one-megohm +/- 10% resistance Static-dissipative table or floor mats with hard tie to ground Field service kits Static awareness labels Wrist straps and footwear straps providing one-megohm +/- 10% resistance Material handling packages Conductive plastic bags Conductive plastic tubes Conductive tote boxes Opaque shielding bags Transparent metallized shielding bags Transparent shielding tubes
4.2
4.2.1
Routine Care
General Cleaning Safety Precautions
1. Never use solvents or flammable solutions to clean the computer. 2. Never immerse any parts in water or cleaning solutions; apply any liquids to a clean cloth and then use the cloth on the component. 3. Always turn off the computer when cleaning with liquids or damp cloths. 4. Always turn off the computer before cleaning the keyboard, mouse, or air vents. 5. Disconnect the keyboard before cleaning it. 6. Wear safety glasses equipped with side shields when cleaning the keyboard.
Compaq Deskpro EN Series of Personal Computers
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4.2.2
Cleaning the Computer Case
Follow all safety precautions in Section 4.2.1 before cleaning the computer. To clean the computer case, follow the procedures described below:
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To remove light stains or dirt, use plain water with a clean, lint-free cloth or swab. For stronger stains, use a mild dishwashing liquid diluted with water. Rinse well by wiping it with a cloth or swab dampened with clear water. For stubborn stains, use isopropyl (rubbing) alcohol. No rinsing is needed as the alcohol will evaporate quickly and not leave a residue. After cleaning, always wipe the unit with a clean, lint-free cloth. Occasionally, clean the air vents on the computer. Lint and other foreign matter can block the vents and limit the airflow.
4.2.3
Cleaning the Keyboard
Follow all safety precautions in Section 4.2.1 before cleaning the keyboard. To clean the tops of the keys or the keyboard body, follow the procedures described in Section 4.2.2. When cleaning debris from under the keys, review all rules in Section 4.2.1 before following these procedures:
CAUTION: Use safety glasses equipped with side shields before attempting to clean debris from under the keys. n n n
Visible debris underneath or between the keys may be removed by vacuuming or shaking. Canned, pressurized air may be used to clean debris from under the keys. Caution should be used as too much air pressure can dislodge lubricants applied under the wide keys. If you remove a key, use a specially designed key puller to prevent damage to the keys. This tool is available through many electronic supply outlets.
CAUTION: Never remove a wide leveled key (like the space bar) from the keyboard. If these keys are improperly removed or installed, the keyboard may not function properly.
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Cleaning under a key may be done with a swab moistened with isopropyl alcohol and squeezed out. Be careful not to wipe away lubricants necessary for proper key functions. Use tweezers to remove any fibers or dirt in confined areas. Allow the parts to air dry before reassembly.
4.2.4
Cleaning the Monitor
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Wipe the monitor screen with a clean cloth moistened with water or with a towlette designed for cleaning monitors. Do not use sprays or aerosols directly on the screen; the liquid may seep into the housing and damage a component. Never use solvents or flammable liquids on the monitor. To clean the monitor body, follow the procedures in Section 4.2.2.
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4-4
Removal & Replacement Preliminaries
4.2.5
Cleaning the Mouse
Before cleaning the mouse, ensure that the power to the computer is turned off.
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Clean the mouse ball by first removing the retaining plate and the ball from the housing. Pull out any debris from the ball socket and wipe the ball with a clean, dry cloth before reassembly. To clean the mouse body, follow the procedures in Section 4.2.2.
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4.3
Service Considerations
Listed below are some of the considerations that you should keep in mind during the disassembly and reassembly of the computer.
4.3.1
Power Supply Fan
The power supply fan is a variable-speed fan based on the temperature in the power supply.
CAUTION: The cooling fan is off only when the computer is turned off or the power cable has been disconnected. The cooling fan is always on in all other instances (when the computer is either in the "On," "Standby," or "Suspend" mode). You must disconnect the power cord from the power source before opening the computer to prevent system board or component damage.
4.3.2
Tools and Software Requirements
To service the computer, you need the following:
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Torx T-15 screwdriver (Compaq screwdriver, part number 161946-001) Flat-bladed screwdriver (may sometimes be used in place of the Torx Screwdriver) Compaq tamper-resistant T-15 wrench (Smart Cover FailSafe Key, PN 166527-001) or Compaq tamper-resistant T-15 bit (Smart Cover FailSafe Key, PN 166527-002) ¼-inch wrench for the speaker nuts Diagnostics software
4.3.3
Screws
The screws used in the computer are not interchangeable. They may have standard or metric threads and may be of different lengths. If an incorrect screw is used during the reassembly process, it can damage the unit. Compaq strongly recommends that all screws removed during disassembly be kept with the part that was removed, then returned to their proper locations.
Compaq Deskpro EN Series of Personal Computers
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4.3.4
Cables and Connectors
Most cables used throughout the unit are flat, flexible cables. These cables must be handled with 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 the cables are routed in such a way that they cannot be caught or snagged by parts being removed or replaced.
CAUTION: When servicing this computer, ensure that cables are placed in their proper location during the reassembly process. Improper cable placement can damage the computer.
4.3.5
Hard Drives
Handle hard drives as delicate precision components, avoiding all physical shock and vibration. This applies to failed drives as well as replacement spares.
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Use only the packaging provided by Compaq for shipping. Do not remove hard drives from the shipping package for storage. Keep hard drives in their protective packaging until they are actually mounted in the CPU. Avoid dropping drives from any height onto any surface.
4.3.6
Plastic Parts
Plastic parts can be damaged by the use of excessive force during disassembly and reassembly. When handling the plastic parts, use care. Do not use a screwdriver or similar tool to pry apart the plastic components; use a flexible tool, like a tongue depressor.
4.3.7
Lithium Battery
The lithium battery that comes with the computer is replaceable and should be properly disposed of.
!
WARNING: Do not abuse or disassemble the lithium battery, as it may explode if mistreated. Do not disassemble, crush, puncture, short external contacts, dispose of in water or fire, or expose it to ° ° temperatures higher than 140 F (60 C).
4-6
Removal & Replacement Preliminaries