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Course ILT
Electricity and power systems
Unit objectives
 Measure and describe the
characteristics of electricity
 Identify static electricity and follow
ESD safe practices when working with
computers
 Describe the purpose and features of
power supplies and install a new
power supply into a PC
 Troubleshoot faulty power supplies
Course ILT
Topic A
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Topic A: Electricity and electronics
Topic B: Static electricity
Topic C: Power supplies
Topic D: Power supply troubleshooting
Course ILT
Electricity characteristics
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Voltage
Current
Alternating or direct current
Resistance and impedance
Power and energy
Course ILT
Activity A-1
Examining the characteristics
of electricity
Course ILT
Electrical safety
 Current can kill
 The 1–10–100 rule
 Calculating current
V=i*r
 Resistance of the human body
Course ILT
Safety precautions
Don’t touch exposed contacts
Touch only insulated handles of tools
Leave covers on equipment
Work one-handed
Don’t stick things into electrical
sockets
 Remove jewelry, watches, etc.
 Keep hands clean and dry
 Don’t work in wet surroundings
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Course ILT
Activity A-2
Considering electrical safety
Course ILT
Digital multimeter
Course ILT
Analog multimeter
Course ILT
Using a multimeter
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Measuring resistance
Measuring voltage
Measuring current
Measuring continuity
Course ILT
Activity A-3
Measuring electrical values
Course ILT
Topic B
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Topic A: Electricity and electronics
Topic B: Static electricity
Topic C: Power supplies
Topic D: Power supply troubleshooting
Course ILT
Static electricity
 Build up of charges
 Static dangers
 Discharge voltages
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3,000+ volts to feel
8,000+ volts to see spark
35,000 volts on a dry day on carpet
1,000 volts can damage electronics
Course ILT
Prevent static build-up
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Don’t shuffle your feet
Increase the humidity
Keep yourself grounded
Wear cotton, not synthetics
Remove carpeting
Use air ionization system
Prevent static discharge
Course ILT
 Equalize charge differences safely
– Unplug the equipment
– Touch its metal chassis or power supply
 Keep yourself and equipment
connected
– Wrist straps and anti-static mats
– Static-safe bags
Course ILT
Static wrist strap
Typical internal components
Course ILT
CD-ROM drive
Power supply
CPU / fan
Adapter card
Motherboard
Hard drive
Slide catches
Course ILT
Slide catch, move to open side of case
Determining which side to open
Course ILT
Open this side to access components
Ports and connectors attached to motherboard
Removable front cover
Course ILT
Alignment holes
Alignment posts
Spring catches
Course ILT
Activity B-1
Opening the computer case while
following proper ESD precautions
Course ILT
Topic C
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Topic A: Electricity and electronics
Topic B: Static electricity
Topic C: Power supplies
Topic D: Power supply troubleshooting
Course ILT
A PC power supply
Course ILT
Voltage selection switch
Course ILT
Typical power requirements
Motherboard
30 W
Memory
10 W / 128 MB
CPU
65 W or more
Hard drive
5 – 15 W
CD-ROM drive
10 – 20 W
Floppy drive
5 – 10 W
Adapter card
5 – 30 W
Course ILT
Standard outputs
+3.3 V
14 A
AGP video cards, motherboard
-5 V
0.3 A
ISA bus adapter cards
+5 V
30 A
Motherboard, CD/DVD drives, hard
drives, PCI adapter cards, Pentium III
and earlier processors
+5 V
0.85 A
“Soft power” switch
-12 V
1A
Older network adapters and serial
ports
+12 V
12 A
CD/DVD drives, hard drives, Pentium
4 and Athlon processors,
motherboard
Course ILT
Power_Good signal
 Signals CPU that power is stable and
sufficient
 +5 V over specific wire
 Must arrive at correct time
Peripheral power connector
Course ILT
 “Molex” connector
Floppy power connector
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 “Berg” connector
SATA power connector
Course ILT
 New, for Serial ATA drives
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Wire colors
 Yellow = +12 V
 Red = +5 V
 Black = ground
Course ILT
Motherboard power connectors
Course ILT
Power supply form factors
ATX/NLX
150 x 140 x 86
millimeters
486 and
Pentium PCs
First with softpower switch
and 3.3V
SFX
100 x 125 x 63.5
millimeters
Pentium PCs
No -5 V output
for ISA cards
WTX
150 x 230 x 86
(single fan)
224 x 230 x 86
(double fan)
Pentium PCs
No -5 V output
for ISA cards
Course ILT
Activity C-1
Examining a power supply
and connectors
Course ILT
Topic D
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Topic A: Electricity and electronics
Topic B: Static electricity
Topic C: Power supplies
Topic D: Power supply troubleshooting
Course ILT
Troubleshooting symptoms
 Computer fails to boot when powered
on, but boots after pressing Ctrl + Alt +
Delete
 Computer intermittently stops working
or reboots
 You don’t have sufficient power
connectors to connect all the devices
you want to install
 Computer fails to boot at all, with no
lights or beeps; fans don’t start
 Computer fails to boot, but fans start
Course ILT
Activity D-1
Troubleshooting power supply problems
Course ILT
Unit summary
 Measured and described the
characteristics of electricity
 Identified static electricity and followed
ESD safe practices when working with
computers
 Described the purpose and featurse of
power supplies; and installed a new
power supply into a PC
 Resolved faulty power supply
problems