1. COMPUTER HARDWARE (Part 5a)
Power Supplies

2. Overview - Explain the basics of electricity
• In this chapter, you will learn to
- Explain the basics of electricity
- Describe the details about powering the PC
- Install, maintain, and troubleshoot power supplies

3. Understanding Electricity

4. Measuring Electricity
• Voltage—pressure of electrons in a wire
- Unit of measurement: Volts (V)
• Current— flow (or amount) of electrons in a wire
- Unit of measurement: Ampere (A)
- When voltage is applied to a wire, electrons flow, producing current
• Wattage—measure of power consumed or needed
- Unit of measurement: Watt (W) W = V * A
• Resistance—impedance or opposition to the flow
- Unit of measurement: Ohm (Ω)

5. Measuring Electricity
• Wire has amperage rating
- Defines how much amperage it can handle
• i.e., 20 amp, 30 amp
- If you exceed amperage
• Wires heat up—may break
• Circuit breakers are heat sensitive
- Sense when amperage exceeds threshold
- Breaks the circuit to stop the flow of electricity

6. Two Types of Current - Electricity provided at wall socket
• Alternating Current (AC)—electrical current flows in both directions
- Electricity provided at wall socket
- Frequency of alternations measured in cycles per second, or hertz (Hz)
• Direct Current (DC)—electrical current flows in one direction
- Electricity provided by batteries

7. Powering the PC : Types of Power
• PCs use DC voltage
• Power companies supply AC voltage
• The power supply in a computer converts high-voltage AC to low-voltage DC

8. Supplying AC
• In the U.S., 115 VAC is standard
• Other countries use 230 VAC
- Many PCs may have a small switch on the back to choose 115 or 230 V (used in other countries)
- Pay attention to this switch, especially when traveling overseas

9. Outlet Voltages - Hot has 115 V - Neutral carries no voltage
• Hot and neutral provide path for AC
- Hot has 115 V
- Neutral carries no voltage
• Ground used for safety
- Returns excess electricity to
ground
Wall outlet

10. Multimeter Basics - Voltage - Resistance - Continuity
• A multimeter (or Volt-Ohm meter: VOM) measures:
- Voltage
- Resistance
- Continuity
• Warning
- Set it properly before measuring
- If not, damage can occur

11. Testing AC Voltage - Hot should be 115 VAC
• Verifies wiring of outlet
- Hot should be 115 VAC
- Neutral completes the circuit
- Ground should go to ground

12. Surge Suppressors
• Surge suppressors provide protection against power surges
• Insert between the power supply and the outlet
• Joule is a unit of electrical energy
- Surge suppressor rated by joules
- Higher joules = better protection
• Some protect more than AC surges
- Phone lines for traditional modems
- Cable connections for cable modems

13. Uninterruptible Power Supply
• An uninterruptible power supply (UPS) provides protection against a power dip or power outage
- Contains a battery that provides continuous AC power
- Provides surge protection and power conditioning
• Constantly charges battery
- All UPSs measured in watts and volts-amps

14. Supplying DC - Converting AC into 5, 12, and 3.3 V DC
• The power supply acts as a step-down transformer
- Converting AC into 5, 12, and 3.3 V DC
- PCs use a 12 V current to power motors on
devices such as hard drives and CD-ROM drives
- PCs use a 5-volt/3.3-volt current to support onboard electronics

15. Power Connectors Original PC Main 4-pin Peripheral Floppy Drive
Power Cable
Power Cable
Power Cable
20-pin ATX Main
24-pin ATX Main
20+4-pin ATX Main
Power Cable
Power Cable
Power Cable

16. Power Connectors 6-pin Auxiliary SATA 4-pin ATX +12V Power Cable
8-pin EPS +12V
4+4-pin +12V
Power Cable
Power Cable

17. Power Connectors 6-pin PCI Express 8-pin PCI Express
Power Cable
Power Cable
Power Cable

18. Power Connectors - Can plug in only one way
• Connectors are keyed
- Can plug in only one way
• Splitters and adapters
- Can create two power connectors from one
- Can convert
Molex to SATA

19. Soft Power CMOS - P1 power connector
• ATX power supplies first to use
- P1 power connector
• Always on when plugged in
- 5 V supplied to motherboard when plugged in
• Configured in
CMOS

20. Power Supply Versions Version Year of Introduction
Included Power Cable Connectors PC
1981
Original PC Main
4-pin Peripheral
ATX
1995
20-pin Main
4-pin Peripheral Floppy Drive
ATX 12V 1.0
2000
20-pin Main
4-pin ATX +12V 4-pin Peripheral Floppy Drive 6-pin Auxiliary
ATX 12V 1.3
2003
20-pin Main
4-pin ATX +12V 4-pin Peripheral Floppy Drive 6-pin Auxiliary SATA

21. Power Supply Versions Version Year of Introduction
Included Power Cable Connectors
ATX 12V 2.0
2003
24-pin Main
4-pin ATX +12V 4-pin Peripheral Floppy Drive
6-pin PCI Express SATA
EPS 12V
2003
24-pin Main
8-pin EPS +12V 4-pin Peripheral Floppy Drive
6-pin PCI Express SATA
PCI Express 2.0
2007
24-pin Main
4-pin ATX +12V 8-pin EPS +12V 4-pin Peripheral Floppy Drive
6-pin PCI Express 8-pin PCI Express SATA

22. Original PC Power Cables
• Introduced in 1981
• Plugged in side-by side, either black to black or sparks to smoked
• Standard 5V and 12V supplies
• Maximum power usage 65 watt

23. 4-pin Peripheral Power Cables
• Introduced during the introduction of the first original PC
• Used for HDDs and other add-ons such as fans, extra video card power, supplemental motherboard power, and case lighting
• Still popular until today but reducing due to the introduction of SATA

24. Floppy Drive Power Cables
• Introduced for the 3.5 inch floppy disks
• Sometimes used as an auxiliary power cable for AGP video cards
• Small connector and 20 awg wires, limited to low current use

25. ATX 20-pin Main Power Cable
• Introduced in 1995 featuring new standards ATX
• Additional 3.3V power supply for newer chips
• Ability to switch on and off without using power switch
• Increase maximum power to 250 Watt

26. ATX 24-pin Main Power Cable
• Introduced in 2000 to increase power lines
• Extension for enhanced PCI Express use
• Ability to work on 20-pin ATX boards
• Increase maximum power to 350~450 Watt

27. EPS 12V Main Power Cable
• Introduced in 2003 originally designed for workstations
• Enhanced 12V features to support multiple CPUs
• Maximum power to 380~450 Watt

28. ATX12V or P4 Connector - Provides more 12 V power - Can be Molex
• Many motherboards require a second, four-wire connector
- Provides more 12 V power
- Can be Molex
- Can be PCI-E

29. IT Technician
Niche Market
Power Supply Form Factors

30. Form Factors - TFX12V, SFX12V, CFX12V, LFX12V
• Niche market power supply form factors
- TFX12V, SFX12V, CFX12V, LFX12V
• Active PFC
- Power Factor Correction
- Common in quality power supplies
- Eliminates harmonics

31. Wattage Requirements
• Every device requires some wattage
- Often starting requirements are higher than running requirements
• Power supplies don’t run at 100% efficiency
- ATX 12 V requires power supplies to be at least 70% efficient
• General recommendation
- Use at least a 400 W power supply
- Enough extra for starting and future growth

32. Installing, Maintaining, and
Troubleshooting Power Supplies

33. Installing - Disconnect wires - Remove 4 standard screws - Remove PS
• Removing
- Disconnect wires
- Remove 4 standard screws
- Remove PS
• To install
- Place PS in case
- Replace screws
- Connect wires

34. ATX Soft Power and CMOS
Some ATX power supplies provide a
• An ATX power supply never turns off
real on/off switch on the back
- Continues to supply 5V to the motherboard as long as it is
connected to the power outlet
• Always unplug an ATX power supply before working on it
Can use a screwdriver or car keys to short the two power jumpers to turn the system on or off in
special circumstances

35. Cooling
• The power supply fan provides basic cooling for the PC
- Fan keeps the voltage regulators cool and provides a constant flow of cool air through the computer
- If power supply fan stops, replace power supply
- Many fans have sensors to
detect when they should run quicker

36. Cooling - Most modern computers have case fans
• Case fan provides extra cooling for PC
- Most modern computers have case fans
- Often plug into Molex connector
- Connector adapters can be used

37. Maintaining Airflow - Keep covers on case
• Keep case closed
- Keep covers on case
- If an expansion card is removed from the PC, be sure to cover the hole with
- Without proper airflow, the CPU can overheat and
destroy itself

38. Reducing Fan Noise - Manually adjustable with knob
• Some fans can be adjusted
- Manually adjustable with knob
- Software adjustable by sensing heat
• Larger fans that spin slower are quieter
• Higher-end fans are quieter
- Use better bearings

39. CMOS Fan Options - Doesn’t control fans
• Can monitor PC’s health by showing temperatures
- Doesn’t control fans
- Can set fan thresholds for alarms

40. Freeware Tool - Allows monitoring of fan speeds - Can set fan speeds
• Speedfan
- Allows monitoring of fan speeds
- Can set fan speeds
- Hundreds of chipsets supported

41. - Sudden death - Slowly over time When Power Supplies Die
• Power supplies fail in two ways:
- Sudden death
• When the fan doesn’t turn and no voltage is present
• Computer simply stops working
- Slowly over time
• Intermittent errors
• Output voltages may exceed specs (± 10%)

42. Power Supply Test
• Put the black lead onto any black wire connection
• Put the red lead onto colored wire
• 12 V ± 10%
to 13.2 V
• 5V ± 10%
- If readings are outside tolerance and symptoms
- 4.5 to 5.5 V
• 3.3 V ± 10%
exist, replace power supply
to 3.63 V

43. Power Supply Test - Plug into motherboard - Plug into tester
• Power supplies need a load
- Plug into motherboard
- Plug into tester
• Check power switches
- If faulty, can turn on
with motherboard jumper

44. power supply When Power Supplies Die Slowly
• Intermittent problems
- Sometimes occur, sometimes don’t
- You could measure voltage now and it’s good;
10 minutes later, system crashes
• A dying power supply can cause
- Random lockups and reboots
- Sporadic boot-up difficulties
• When you encounter intermittent symptoms, consider replacing the
power supply

45. Fuses and Fire - Sense when amperage exceeds threshold
• Circuit breakers are heat-sensitive
- Sense when amperage exceeds threshold
- Breaks the circuit to stop flow of electricity
• Fuses blow for a reason
- Power supply is malfunctioning
- As a designed safety precaution, fuses blow (break) to stop circuit
• Alternative is a possible fire

46. Fire Extinguishers - Ordinary combustibles such as paper and wood
• Class A
- Ordinary combustibles such as paper and wood
• Class B
- Flammable liquids such as gasoline
• Class C
- Live electrical equipment
• Use only Class C extinguishers on electrical fires

47. Beyond A+ - Fancy colors, light up, and have extra fans
• It glows
- Fancy colors, light up, and have extra fans
• Module power supplies
- Reduced cables
• Rail power
- Look for power supplies that offer 16 to 18 A per 12 V rail