1. Electricity and power supplies
Unit objectives:
Identify electrostatic discharge, and follow ESD safe practices while working with computer components
Install a new power supply in a PC
Troubleshoot faulty power supplies

2. Topic A Topic A: Electrical safety Topic B: Power supplies
Topic C: Power supply troubleshooting

3. Characteristics of electricity
Electricity — Flow of electrons
Conductor — Permits flow of electricity
Insulator — Inhibits flow of electricity
Voltage — Force of electricity caused by difference in charge at two locations
Measured in volts
Also called “potential” or “potential difference”
Officially designated as uppercase V
May see it as lowercase v
continued

4. Characteristics, continued
Current — Measure of the flow of electrons past a given point
Measured in amps, or amperes
Must be a complete circuit (closed circuit)
Direct current — Flows in one direction, at constant voltage, through circuit
Alternating current — Flows repeatedly back and forth through the circuit, at constantly varying voltage levels
continued

5. Characteristics, continued
Resistance — Force that opposes the flow of DC through a conductor
Measured in ohms (Ω)
Impedance — Like resistance, but applies to AC
Power
Measured in watts
Calculate by multiplying voltage by current
Energy — Electrical power delivered over time

6. Examining the characteristics of electricity
Activity A-1
Examining the characteristics of electricity

7. Electricity Current can kill The 1–10–100 rule Calculating current
V = i * r
Resistance of the human body is about 500 KΩ (500,000 Ω)

8. Safety precautions Don’t touch exposed contacts
Touch only insulated handles of tools
Leave covers on equipment
Work one-handed
Don’t insert anything into wall outlets
Remove jewelry, watches, etc.
Keep hands clean and dry
Don’t work in wet surroundings

9. Considering electrical safety
Activity A-2
Considering electrical safety

10. Electrostatic discharge (ESD)
Buildup of charges
Static dangers
Discharge voltages
3000+ volts to feel
8000+ volts to see spark
35,000 volts on a dry day on carpet
30 volts can damage electronics

11. Preventing static buildup
Don’t shuffle your feet
Increase the humidity: 50-60%
Keep yourself grounded
Wear cotton, not synthetics
Remove carpeting
Use air ionization system

12. Preventing static discharge
Equalize charge differences safely
Unplug the equipment
Touch the metal chassis or power supply
Keep yourself and equipment connected together
Wrist straps and antistatic mats
Static-safe bags
Goal is to be at a charge potential that’s equal with the device you’re servicing (not with ground)
Service on a properly grounded bench

13. Antistatic (ESD) wrist straps

14. Typical internal components
Power supply
CD-ROM drive
Hard drive
CPU/fan
Motherboard
Adapter card

15. Slide catches
Slide catch, move to open side of case

16. Determining which side to open
Open this side to access components
Ports and connectors attached to motherboard

17. Removable front cover
Alignment holes
Alignment posts
Spring catches

18. Opening the computer case while following proper ESD precautions
Activity A-3
Opening the computer case while following proper ESD precautions

19. Topic B Topic A: Electrical safety Topic B: Power supplies
Topic C: Power supply troubleshooting

20. PC power supply
Converts AC wall voltage to DC voltages for PC components
Includes a fan
Provides some conditioning functions
Can maintain power during brief drops and outages

21. Power supply specifications
Rated by DC power output in watts
Modern systems typically =>300 watts
Older systems <200 watts
Rating isn’t an indicator of power draw
Draws only the power needed to supply internal components

22. Typical power requirements
Motherboard
30 W
Memory
10 W per 2 GB
CPU
45–145 W or more
Hard drive
5–15 W
CD-ROM drive
5–20 W
Floppy drive
5–10 W
Adapter card
5–30 W

23. Standard outputs
+/- 5 V
+/- 12 V
+ 3.3 V

24. Power connectors Two standards Drive power connectors
Motherboard power connectors

25. Peripheral power connector
Molex connector
Typically used to connect hard drives and optical drives

26. Floppy power connector
Berg connector
Smaller than Molex
Typically used to connect floppy drives

27. SATA power connector
New, for Serial ATA drives

28. Wire colors Wire color Molex Berg SATA Voltage Yellow 1 4 13, 14, 15
Red
1 (optional)
7, 8, 9
+5 V
Black
2 and 3
2 (optional) and 3
4, 5, 6 10, 11,12
Ground
Orange
1, 2, 3
+3.3 v

29. Motherboard power connectors
Single power connector
Dual power connectors (P8/P9)

30. Power supply form factors
Describes size and shape
Must fit:
Case
Motherboard
Other components

31. Identifying your computer’s power supply
Activity B-1
Identifying your computer’s power supply

32. Installing a power supply
Shut down computer
Unplug computer
Remove cover from computer
Disconnect all power wires from components, including motherboard
Remove retaining screws
Remove power supply
Install new power supply and screw it into place
Connect power wires to components as needed, including motherboard
Replace cover
Plug computer into outlet, and boot system to test your work

33. Selecting the voltage
Set power supply to run on VAC or VAC
With computer off, slide switch
Usually located near power cord port
continued

34. Selecting the voltage, continued
Improperly set voltage, can cause computer to:
Fail to turn on
Operates improperly
Incur serious damage

35. Installing a new power supply
Activity B-2
Installing a new power supply

36. Topic C Topic A: Electrical safety Topic B: Power supplies
Topic C: Power supply troubleshooting

37. An AC signal

38. Power problems Blackout — Total loss of power
Brownout — Brief decrease in voltage level
Noise — Disruption of smoothly varying AC signal
Spike — Very brief increase in voltage
Surge — Brief increase in voltage (longer than spike)

39. Power conditioning Surge protectors Battery backup devices Generators
Filter out spikes and surges
Battery backup devices
Condition the power signal
Some protect against brownouts
Continuous UPS vs. standby UPS
UPS monitoring and management software
Generators
Provide power for extended periods
Use a variety of fuels
Computer-grade generators produce clean, consistent AC signals

40. Discussing power conditioning equipment
Activity C-1
Discussing power conditioning equipment

41. Electrical measurements
Measure electrical values with a multimeter
Multimeters can be digital or analog
Use to measure
Resistance
Voltage
Current
Continuity

42. Measuring resistance
Turn off the device you’re measuring and disconnect it from its power source
You might need to disconnect the device from its circuit
Set the multimeter to read resistance
Touch the two leads of the multimeter together
Touch the black and red probes to either side of the circuit to be measured
Read the resistance from the meter’s display

43. Measuring voltage Verify the power supply is on
Set your multimeter to read either DC or AC voltage
Touch the black probe to the ground, and touch the red probe to the spot where you want to measure the voltage
Read the voltage from the meter’s display
You must exercise care when taking voltage readings as the computer is powered up

44. Measuring current Break the circuit and insert the meter in the break
Ammeter doesn’t require break
Clamp ammeters are often used to measure current flow in 110 V and higher circuits

45. Measuring continuity
Set your multimeter to display resistance (ohms) and look for circuits with zero resistance
Also can use continuity mode, if available

46. Power supply tester Alternative to manual test with multimeter
Takes approximately 30 minutes
Follow instructions for your specific tester
Advantages:
Less susceptible to human error
Results are more conclusive
Safer to perform

47. Measuring electrical values
Activity C-2
Measuring electrical values

48. Power supply problems
Computer fails to boot when powered on, but boots after Ctrl+Alt+Del
Computer intermittently stops working or reboots
You don’t have enough power connectors for all the devices you want to install
Computer fails to boot at all (no lights or beeps); fans don’t start
Computer fails to boot, but fans start

49. The Power_Good signal Signals CPU that power is stable and sufficient
+5 V over specific wire
Must arrive at correct time

50. Troubleshooting power supply problems
Activity C-3
Troubleshooting power supply problems

51. Electricity and power supplies
Identified electrostatic discharge, and followed ESD safe practices while working with computer components
Installed a new power supply in a PC
Resolved problems with faulty power supplies