Assembly / Disassembly / Reassembly

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Assembly / Disassembly / Reassembly

• Computers

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Chapter Objectives

• After completing this chapter you will
• Understand how static electricity can damage a
  computer.
• Understand what type of equipment causes RFI and
  EMI.
• Know which tools a technician needs.
• Understand the importance of diagramming when
  disassembling a computer.
• Be able to disassemble and reassemble a computer.

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Disassembly Overview

• Seldom is it necessary to completely disassemble
  a computer, however when a technician is first
  learning microcomputers, it can be both very
  informative and fun.
• Sometimes disassembly is accomplished to perform
  a preventive maintenance cleaning.
• Other instances where disassembly is helpful is
  in diagnosing a problem of undetermined cause by
  removing components one by one or to outside the
  case. It can also help with diagnosing grounding
  problems.
• Grounding Occurs when motherboard or adapter
  isnt properly installed and a trace (metal line
  on the motherboard or adapter) touches the
  computer frame and causes the adapter or other
  components to stop working.

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Electrostatic Discharge (ESD)

• ESD (ElectroStatic Discharge) Occurs when
  stored up static electricity is discharged in an
  instantaneous surge of voltage. ESD damage is
  nonrecoverable and the most susceptible
  components are the CMOS and RAM chips.
• Anti-static Wrist Strap A strap connecting the
  technician to the computer and that equalizes the
  voltage potential between the two to prevent ESD.
  It is connected to a grounding post or a metal
  component such as the power supply. Electronic
  symbol for ground is
• Warning A technician should NEVER wear an ESD
  wrist strap when working inside a monitor because
  of high voltages!

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Electrostatic Discharge (ESD)
Anti-Static Wrist Strap
Disassembly Figure 1
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EMI (Electromagnetic Interference)

• EMI (ElectroMagnetic Interference) also called
  EMR (ElectroMagnetic Radiation) is noise caused
  by electrical devices. Can travel through
  electrical wires.
• RFI (Radio Frequency Interference) Noises that
  occur in the radio frequency range.
• Always replace the slot covers for expansion
  slots that are not being used. This will keep
  out dust and improve the airflow inside the
  computer.

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Tools

• Having the proper tools to disassemble the
  computer can make the task easier and prevent
  damage to computer components.

8
Reassembly

• Reassembly is easily accomplished if the user is
  careful and diagrams properly during disassembly.
  Exercise care and reinstall all components to
  their original location.
• Three major reassembly components are
• Motherboards have plastic connectors on the
  bottom called standoffs.
• Cables
• Connectors
• Standoffs Plastic connectors on the bottom side
  of a motherboard that attach it to the case and
  prevent it from being in contact with the metal
  of the computer case.

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Cables and Connectors

• Keyed A connector or cable that has an extra
  metal piece that allows correct connections.
• Pin 1 Pin 1 on a cable should be connected to
  Pin 1 on the connector. The colored stripe on
  the edge of the cable identifies Pin 1 on the
  cable.
• Pin 1 on an adapter will be stenciled beside the
  connector.
• Solder Joints Solder connections on the back of
  motherboards and adapters. Pin 1 solder joints on
  the back of connectors are square.
• Hot wire Brings AC current from the power
  supply to the PCs front panel.
• Return wire Returns AC current from the PCs
  front panel to the power supply.

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Cables and Connectors
Ribbon Cables Pin 1
Disassembly Figure 2
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Cables and Connectors
Adapters Pin 1
Disassembly Figure 3
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Cables and Connectors
Disassembly Figure 4
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Cables and Connectors
Connectors Pin 1
Disassembly Figure 5
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Cables and Connectors
Front Panel Power Switch Connections
Disassembly Figure 6
15
Hard Drives

• Hard drives must be handled carefully during
  disassembly because of the delicate nature of
  their very intricate construction.
• The read/write heads are located only millimeters
  from the platter storing all the data. A small
  jolt can cause them to make contact with the
  platter and cause permanent physical damage.
• Older hard drives had utility programs to park,
  or lock, the heads in place away from the
  platters when not in use.
• Self-Parking Heads Hard drives that have
  read/write heads which pull away automatically
  when the computer powers off. This feature still
  would not prevent damaged caused by an accident
  or mishandling.

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Preventive Maintenance

• Preventive Maintenance Certain procedures
  performed to prolong the life of the computer,
  such as cleaning the computer, drive heads,
  keyboard keys, printers, and monitor screen.
• MSDS (Material Safety Data Sheets) Sheets that
  contain information about a product, its
  toxicity, storage, and disposal.