Download Lab 4 - Dr. Feda A. AlShahwan

Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section
PC Maintenance 205
Exercise # 4
Power Supply
Objective:
 When you have completed this lab you will know how to test a computer
power supply to verify that it is working correctly.
 You will be able to identify the different power supply connectors that
distribute power to various components.
Required tools:
 Test resistor
 Small container for the screws
 Small flash light
 Magnifying Glass
 Digital Multimeter
Safety issues
 Do not use the antistatic wrist strap when working with power supply or
monitor.
 Do not work inside the power supply it is dangerous.
 When removing cables from their respective sockets remove them gently from
their sides.
 When inserting cables into their respective sockets do not force them if they
are not fitting. This will bend the pins. Notice the red stripe should be
connected to pin number 1
Description of power supply:
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Some call a computer's microprocessor the computer's brain. Well if the CPU
is the brain, then the power supply is its heart. The power supply provides the
required voltages and currents to operate the computer.
In effect the power supply is an electrical energy converter. It converts the AC
line voltage into a regulated DC voltage for computer operation.
Exercises:
Identifying power supply external components:

In this procedure, you will identify the external power supply components that
can be viewed from the back rear of your computer case.
____________________________________________________________________
Dr. Feda AlShahwan
1
Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section


PC Maintenance 205
Look at the rear of the chassis and identify the power supply external
components.
List down the external components:
_________________
_________________
_________________
_________________
Setting up the Input Voltage Selector Switch:

In this procedure, you will check the outlet voltage level and setup the input
voltage selector switch to match it.
_____________________________________________________________________
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Using the multimeter measure the voltage of the outlet socket.
Outlet Socket Voltage: _________________
Check the Input Voltage Selector Switch. There are two possible Input
Voltage Range settings. The Low range is from 110 to 120 Volts AC. The
High range is from 220 to 240 Volts AC. In the United States, the Low range
is used.
The Input Voltage Selector Switch is marked with a value for each range. The
specific numbers used to mark the switch will vary between Power Supplies.
Check the position of the Input Voltage Selector Switch in you PC.
Input Voltage Range: _____________
If you are in the United States or another country that uses 110 to 120 Volts
AC, move the Switch to the Low range position, if it is not already set there.
The marking should be 110, 115 or 120. This marking will be visible when the
Switch is in the Low range position.
If you are in Kuwait or another country that uses 220 to 240 Volts AC, move
the Switch to the High range position, if it is not already set there.
The marking should be 220, 230 or 240. This marking will be visible when the
Switch is in the High range position.
Dr. Feda AlShahwan
2
Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section
PC Maintenance 205
Identifying power connectors:

In this procedure, you will identify the type and number of power connectors
in your computer.
1. Remove the right side panel from your computer case. You may find it easiest to
place the case on its side before removing the panel. The motherboard mounting
plate may not be secured inside the case. So, slowly tip the case on its side.
DO NOT remove the front panel.
2. Remove gently all the power connectors from their slots but before doing this
sketch in the following box their locations and how they are connected.
3. Carefully gather together all the power connectors leading from the power supply.
4. in the table below:
A. Place a check mark (..J) next to each type of power connector in your case in the
“In My Case “column.
B. Write how many of each type of power connector are in your case in the
Quantity column.
Dr. Feda AlShahwan
3
Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section
Quantity
PC Maintenance 205
In My Case (..J) Connector Type
ATX 20-Pin Motherboard Power
P8: AT 6-Pin Motherboard Power
P9: AT 6-Pin Motherboard Power
Large 4-Pin DC Power
Medium 4-pin DC Power
Fan connector
Auxiliary 12V connector
Determining the Power Supply rating:
In this procedure, you will identify the power supply parameters.
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Remove the power supply by unscrewing the green screws (one of them is
inside the case and the other is outside).
Read the message in the power supply label that is written in many different
languages and write it in the following space:
Text in English: ________________________________

Fill out the following table from the numbers written in the table:
Item
Value
Form Factor
Power Supply rating
AC input voltage rating
AC input current rating
AC input frequency
Manufacturer
Testing ATX Power Supply:
 In this procedure, you will test the power supply in your computer.
_______________________________________________________________
ATX power supplies have only one motherboard power connector.
Testing +5 VOLTS DC:
1. Adjust the voltmeter to read 20 VDC.
2. Remove the test resistor and shorting wire from the hardware parts package.
Dr. Feda AlShahwan
4
Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section
PC Maintenance 205
Caution:
 The test resistor, which is used to provide a load for the power supply, will get
hot. Be careful to not touch the resistor until it has had time to cool. Also,
position the resistor away from any part that may be damaged by heat.
 For safety, make sure that neither the resistor nor any bare wires are touching
the case, power supply, or each other.
3. Locate the 20 pin ATX power supply connector. Place the shorting wire between
pins 13 & 14.
5. Insert one test resistor lead into ATX power connector pin 3(black wire).
6. Insert the other resistor lead into ATX power connector pin 20(red wire).
7. Connect the red (+) multimeter lead to the resistor lead that is connected to the
pin 20 (red wire).
8. Connect the black (-) multimeter lead to the resistor lead that is connected to the
pin 3 (black wire).
9. Plug the AC power cord into the AC input connector on the computer.
10. Plug the other end of the AC power cord into an AC outlet.
11. Record the voltage reading: _______________
12. The voltage reading should be between 4.90 and 5.15 VDC.
13. Unplug the AC power cord from the outlet.
Testing +5 VOLTS DC:
1. Move the red (+) multimeter lead to the ATX power connector pin 19(red wire).
2. Plug the AC power cord into an AC outlet.
3. Record the voltage reading: ______________
4. The voltage reading should be between -4.75 and -5.15 VDC.
5. Unplug the AC power cord from the outlet.
Testing +12 VOLTS DC:
1. Move the red (+) multimeter lead to the ATX power connector pin 10 (yellow
wire).
2. Plug the AC power cord into an AC outlet.
3. Record the voltage reading: ______________
4. The voltage reading should be between 11.2 and 12.5 VDC.
5. Unplug the AC power cord from the outlet.
Testing -12 VOLTS DC:
1. Move the red (+) multimeter lead to the A TX power connector pin 12 (blue
wire).
2. Plug the AC power cord into an AC outlet.
3. Record the voltage reading: _______________
4. The voltage reading should be between -10.4 and -12.5 VDC.
5. Unplug the AC power cord from the outlet.
6. Disconnect both meter leads and remove the test resistor and shorting wire.
7. Unplug the AC power cord from the computer.
Dr. Feda AlShahwan
5
Public Authority for Applied Education
College of Technological Studies
Electronic Engineering Department
Computer Section
PC Maintenance 205
Testing +3.3 VOLTS DC:
1. Move the red (+) multimeter lead to the ATX power connector pin 2 (orange
wire).
2. Plug the AC power cord into an AC outlet.
3. Record the voltage reading: _______________
4. The voltage reading should be between 3 and 4 VDC.
5. Unplug the AC power cord from the outlet.
6. Disconnect both meter leads and remove the test resistor and shorting wire.
7. Unplug the AC power cord from the computer.
Questions
1. Why do you use test resistor?
2. Why should you short circuit pins 13 and 14?
Dr. Feda AlShahwan
6