course ilt electricity and power systems unit objectives measure and describe the characteristics of...
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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
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Topic A
Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting
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Electricity characteristics
Voltage Current Alternating or direct current Resistance and impedance Power and energy
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Electrical safety
Current can kill The 1–10–100 rule Calculating current
V = i * r Resistance of the human body
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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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Using a multimeter
Measuring resistance Measuring voltage Measuring current Measuring continuity
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Topic B
Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting
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Static electricity
Build up of charges Static dangers Discharge voltages
– 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
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Prevent static build-up
Don’t shuffle your feet Increase the humidity Keep yourself grounded Wear cotton, not synthetics Remove carpeting Use air ionization system
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Prevent static discharge
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
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Typical internal components
Power supply
CD-ROM drive
Hard drive
CPU / fan
Motherboard
Adapter card
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Determining which side to open
Ports and connectors attached to motherboard
Open this side to access components
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Topic C
Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting
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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
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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 1 A Older network adapters and serial ports
+12 V 12 A CD/DVD drives, hard drives, Pentium 4 and Athlon processors, motherboard
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Power_Good signal
Signals CPU that power is stable and sufficient
+5 V over specific wire Must arrive at correct time
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Power supply form factors
ATX/NLX 150 x 140 x 86 millimeters
486 and Pentium PCs
First with soft-power 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
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Topic D
Topic A: Electricity and electronics Topic B: Static electricity Topic C: Power supplies Topic D: Power supply troubleshooting
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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
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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