Assembly / Disassembly / Reassembly

Computers

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.

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 isn’t 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.

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!

Electrostatic Discharge (ESD)

Anti-Static Wrist Strap

Disassembly – Figure #1

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.

Tools

Having the proper tools to disassemble the computer can make the task

easier and prevent damage to computer components.

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.

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 PC’s front

panel.

• Return wire – Returns AC current from the PC’s front panel to the power

supply.

Cables and Connectors

Ribbon Cable’s Pin 1

Disassembly – Figure #2

Cables and Connectors

Adapter’s Pin 1

Disassembly – Figure #3

Cables and Connectors

Disassembly – Figure #4

Cables and Connectors

Connector’s Pin 1

Disassembly – Figure #5

Cables and Connectors

Front Panel Power Switch Connections

Disassembly – Figure #6

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.

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.