2. 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.
3. 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.
4. 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!
6. 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.
7. 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.
9. 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.
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.
16. 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.
