Mobile Phone Repair and Maintenance

Table of Contents
................................................................................................4
ABBREVIATIONS AND ACRONYMS

REPAIR AND
MOBILE CELL PHONE REPAIR AND MAINTENANCE ........................................................................5

.....................................................................................................................5
Introduction

...........................................................................................................6
TYPES OF MOBILE PHONES

MAINTENANCE OF ..................................................................................................6
What is a mobile phone?
....................................................................................................6
Types of Mobile Phones
......................................................................................................7
What is a form factor?

MOBILE CELL PHONES .................................................

POTENTIAL HAZARDS ASSOCIATED WITH MOBILE PHONE REPAIR 9

.............................................................................................................9
What is a hazard?

PARTS OF A CONVENTIONAL MOBILE ..............................................................................

PHONE 11

...................................................................................................13
MOBILE PHONE REPAIR TOOLS

Factors to Consider When Choosing Mobile Phone Repair ........................................

tools 13
........................................................................................ 13
Tools for Mobile Phone Repair

........................................................
DISASSEMBLING AND ASSEMBLING A MOBILE CELL PHONE 19

..................................................................................................19
What is to disassemble?
......................................................................................................19
What is to assemble?
Disassembling A Mobile Phone ........................................................................................20
Assembling a Mobile Phone ............................................................................................ 22

DIAGNOSING AND REPAIRING MOBILE PHONE...............................................................

FAULTS 23

Skills Needed to Diagnose and Repair a Mobile ......................................................

Phone 23
..................................................................................................27
Mobile Phone Diagnosis

............................................................................30
REPAIR OF COMMON MOBILE PHONE FAULTS

.............................................................................................................. 30
What is a fault?
.............................................................................................................. 42
Software Faults
 Mobile Phone Repair and Maintenance

Abbreviations an
3G: 3Rd Generation in Mobile Telephony
AC: Alternate Current.
BGA: Ball Grid Array
BSI: Battery Status Indicator
CDMA: Code Division Multiple Access
CPU: Central Processing Unit
DCT: Digital Core Technology
DC: Direct Current
ESD: Electro Static Discharge
FM: Frequency Modulation
GSM: Global System For Mobile phones
IC: Integrated Circuit
IMEI: The International Mobile Station Equipment Identity
LCD: Liquid Crystal Device
LED: Light Emitting Diode
MIC: Microphone
PDA: Personal Digital Assistance
PCB: Printed Circuit Board
PFO: Power Frequency Oscillator
RAM: Random Access Memory
RTC: Real Time Clock
SMD: Surface Mount Device
SIM: Subscriber identification module
 Mobile Phone Repair and Maintenance Mobile Phone Repair and
Maintenance

Mobile Cell Phone Repair and Types of Mobile phones

Maintenance What is a mobile phone?
Introduction A mobile phone is a handheld device that allows you to make and
receive telephone calls while you move around a wide geographical
area. A mobile phone also supports several other functions, such as text
Welcome to this course on mobile cell phone repair and maintenance. A mobile cell messaging, email and internet access, photography, money transfer,
phone is a hand held mobile device that can perform several communication banking, and so on.
functions. Mobile technology has become one of the fastest growing technologies in
the world. Today people use mobile phones to stay in touch with friends and family,
to share stories and photographs in social media, and to carry out financial Types of Mobile Phones
transactions.
Well, there is no general rule used to classify mobile cell phones. However, in most
This widespread ownership and use of mobile phones has created a need for cases they are classified on the basis of their form factor.
professionals who can repair and service mobile phones. This unit targets people
who would like to start and run a mobile repair and servicing business. By the end
of this course unit you should be able to disassemble and assemble a mobile phone, What is a form factor?
diagnose the problem, service and repair a mobile phone with the help of proper
tools and instruments. A form factor refers to the size, style, and shape of a mobile phone, as well as to the
layout and position of the phone's major components. There are four major forms of
mobile phones, namely:
Learning Outcomes • The bar phone,
• The touch screen phone
Upon completion of this course you will be able to: • The flip phone, and
• Identify different types of mobile cell phones • The slider phone.
• Recognise potential hazards in the repair of mobile cell phones
• Identify the parts of a mobile cell phone
• Use the correct hardware tools to repair mobile cell phones
• Assembly and disassembly a mobile cell phone
• Identify mobile cell phone faults and solve them.
 Mobile Phone Repair and Maintenance

The Bar Phone

A bar phone is also known as the slab,
block, or slate phone. It takes the shape The Flip Phone
of a cuboid, usually with rounded corners A flip or clamshell phone consists of two
and/or edges. The name is derived from or more sections that are connected by
the rough resemblance to a candy bar in hinges, as shown in figure 3. The hinges
size and shape, see Figure 1 below. allow the phone to flip open and fold to
close in order to become more compact.
When flipped open, the phone's speaker
and microphone are placed closer to the
Figure 1: A bar phone
operator's ear and mouth, thereby
improving usability.

Figure 3: A flip phone

The Touch screen Phone
A touch screen, or slate phone is a
subset of the bar form. Like the tablet
computer, a touchscreen phone has The Slider Phone
minimal buttons and instead relies on an A slider or slide phone is composed of
electronic visual display known as a usually two, but sometimes more,
touch screen. It also has an onscreen sections that slide past each other on
QWERTY keyboard. rails. It usually has a display segment
which houses the speaker and screen,
while the segment that slides in and out
QWERTY refers to the arrangement of contains the keypad or keyboard. The
keys or buttons on an English sliding form factor allows the owner to
computer keyboard. take advantage of a full key board
without sacrificing portability. Figure 4
Figure 2: Touch screen phone Figure 4: A slider phone shows a picture of a slider phone.
Figure 2 shows a picture of a
touchscreen phone.

We hope you now understand the various types of mobile phones. Let us now look at
the potential hazards that are associated the repair of a mobile phone.
 Mobile Phone Repair and Maintenance
Parts of a Conventional Phone
Potential Hazard with Mobile Phone A mobile phone has several parts or components. It is important
for you to know the parts and understand their functions so that
Your physical well being is important not only to yourself, but also to others.
you can easily diagnose and solve problems. How many parts of a
Therefore, as you embark on mobile phone repair, you should be aware of all
mobile phone do you know? Take a minute to think about it and
the potential hazards and how to prevent them.
then complete the following activity.

What is a hazard? A conventional mobile phone is made up of many parts. Table 2

A hazard is anything that has the potential to cause harm to yourself or those below explains the functions of the main parts.
around you. Before you learn the difference some of the terms associated with
hazards. Write down the meaning of the terms in the following activity. Table 2: Parts of a mobile phone and their functions

There are quite a number of potential hazards that one can encounter when Parts of a mobile cell phone Functions
servicing or repairing a mobile phone. These are listed in Table 1 together with Used for inputting or entering data into the phone. It is
Keypad
the preventive actions that you could take to avoid them. connected directly to the CPU
Ear piece Converts the electric signal to a sound signal
Table 1: Potential hazards during mobile phone repair and their prevention Mouth piece Transmits sound from one phone to another
Hazard Preventive Actions Battery Source of power supply to a mobile phone
Power switch Switches the phone on and off
Use of well insulated tools
Burns Use of gloves
Keeping the soldering iron in the right place Power IC It takes power from the battery and supplies to all other
parts of a mobile phone
Unplugging equipment when not in use
Oscillator It creates frequency during outgoing calls
Appropriate storage of equipment
Displays data. It is connected to the CPU to receive
Pricks by sharp objects Proper disposal of sharp objects
following signals : LCD Data Signal, LCD Reset Signal, LCD
Use of appropriate tools and equipment Screen or display
WR Signal, LCD RD Signal, LCD FLM Signal, LCD HSYN Signal
etc.
Proper disposal of electronic wastes
Environmental pollution Make sure electrical equipment is unplugged while Flash IC Stores the software and other programs installed in the
Trailing electrical cablesnot in use mobile phone
Safe storage of cables Charging IC Takes the current from the charger and charges the battery
Falls Keep all tools, bins etc. in the right place CPU Controls all sections of a mobile phone

Antenna Receives and transmit radio frequencies and helps the

Having looked at potential hazards and how to protect ourselves during phone to connect to the cellular network
mobile phone repair, let us now consider the parts of a mobile phone.
Figure 5 below shows a printed circuit board (PCB) of a mobile phone showing
the different internal parts. As you can see from this diagram the PCB is divided
into two parts, the network section and the power section. The network section
controls the incoming and outgoing phone calls, while the power section
controls the memory and power related functions of the phone.
 Tools for Mobile Phone Repair
Below are the tools and equipment needed for mobile phone repair.

Mobile Phone Repair and Maintenance

1. Soldering Iron: Used to solder small

components like capacitor, resistor,
diode, transistor, regulator, speaker,
microphone, display etc. A 50 watt
soldering iron is good enough for
most mobile phones repairing job.

Figure 6: Soldering iron

Figure 5: Parts of a mobile phone

Make sure that you learn them well and are be able to locate them easily
before you move on to the next section. Let us now look at the tools that you
need to repair mobile phones. 2. PCB Holder / PCB Stand
(Printed
Circuit Board): PCB is used to hold the
PCB of a mobile phone while soldering
or repairing. It holds the PCB very

Mobile Phone Repair strongly and doesn’t all thus helping in

repairing.

Figure 7: PCB holder

There are hundreds of tools for mobile phone repair available in
the market. It is important to select the best tool that enables
you to repair the phone easily and comfortably.

Factors to Consider When Choosing Mobile Phone Repair tools

3. Solder Wire: used to solder electronic
When selecting tools and equipment for repairing mobile cell components, ICs or jumpers. The
phones, you should consider the following factors: composition of most solder wire is Tin /
Lead in the ratio 60:40 or 63:37.
1. Cost
2. Brand Figure 8: Solder wire
3. Quality/ Durability
4. Availability
5. Suitability
4. Thinner or PCB Cleaner:
Thinneror
PCB cleaner is used to clean the PCB
of a mobile phone. The most common
PCB cleaner used in mobile phone
repairing is IPA or Isopropyl Alcohol.
It is important to buy only good
quality PCB cleaner as poor quality
PCB cleaners can damage the system
board.
Figure 9: Thinner or PCB cleaner
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

11. Brush:These are used for cleaning the

5. Jumper Wire: This is a thin laminated PCB of a mobile phone when it is
or coated copper wire used to jumper being repaired. It is important to buy
from one point to another on the track only ESD-Safe cleaning brushes.
of a mobile phone during repair.
Figure 16: Brushes
Figure 10: Jumper wire

6. Point Cutter:
It is used for cutting 12. Multimeter
: an electronic measuring
device that has the ability to measure
voltage, current and resistance. It is
used to test and check the readings
Figure 11: Point cutter of various parts and components of a
mobile phone.

Figure 17:Digital Multimeter (Source:

7. Blade Cutter
: This is used to commons.wikipedia.org)
remove lamination from jumper
wire. It can also be used for several
other purposes.
Figure 12: Blade cutter
13. Hot Air Blower
: It isalso called SMD
(Surface Mount Device) rework
system and SMD repair system. It
has control to regulate or manage
temperature and flow or hot air.
Always buy a good quality ESD-Safe
hot air blower.
8. Nose Cutter: this is used for cutting.
Figure 18: Hot air blower

Figure 13: Nose Cutter

9. Precision Screwdriver: It is used to

14. Battery Booster: It is used to
remove and tighten screws while
boost the power of battery of a
assembling and dissembling a mobile
mobile phone.
phone. Precision screwdrivers of sizes
T4, T5, T6 and forehead are good for
most mobile repairing job. Figure 14: Precision screwdriver
Figure 19: Battery booster

10. Tweezers: These are needed to hold

electroniccomponents, ICs, jumper
wire etc. while soldering and
Desoldering. Figure 15: Tweezers
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

19. Cleaning Sponge

: this is used to
15. Screwdriver Kit: It has several cleanthe tip of soldering iron while
screwdrivers of different shapes soldering.
and sizes to disassemble and
assemble a mobile phone. Figure 24: Cleaning sponge

Figure 20: Assorted screwdrivers

20. Solder Paste: The solder paste is a
low melting metal used to join
together metal work pieces. It has a
lower melting point than the metal
work pieces.
16.Microscope: It is used to see a
magnified view of PCB or electronic Figure 25: Solder paste
components. These are available in
different zoom options. Many
microscopes can also be connected
to a computer or a monitor.

Figure 21: Microscope

21. LCD Tester

: Used to check whether
the LCD screen of a mobile phone
17. Test JIG Box
: This device is used to is faulty or not.
diagnose and find fault or problem in
a mobile phone. It helps the mobile
phone to work and function normally Figure 26: LCD tester
outside its case. This helps to test and
check voltage and other test points on
the PCB. In simple words it helps the
mobile phone to work without
battery. You now know the main tools that are used to repair a mobile phone. In the next
Figure 22: Test JIG box section we shall discuss how to disassemble and assemble a mobile phone.

18. Battery Tester: This

device is used
to test and analyze the status or
condition of the battery of a mobile
cell phone.

Figure 23: Battery tester

 Mobile Phone Repair and
Maintenance
Internal Parts of a Mobile Phone

Disassembling an Mobile Cell Phone Table 3 below outlines the main sections and how they are connected.

Table 3: Internal parts of a mobile phone

Internal Section Connections

What is to disassemble? SIM Card Interface section is directly connected
with the CPU in most mobile cell phones. If there is
To disassemble is to take something apart or to break it down into pieces.
SIM card section no power supply in a mobile phone then the SIM
section is connected with the CPU through the
What is to assemble? Power IC.
In most phones the micro SD card holder is
To assemble is to fit together all the separate pieces in order to form one whole. Memory card section connected through a 8-pin socket. The memory
card section is found inside the CPU
In modern mobile cell phones which have a
separate ear speaker, the speaker is directly
Disassembling a Mobile Phone connected to the CPU. It receives sound via signals
directly from the CPU of from the audio section
The following are the steps that you should take when disassembling a Ear Speaker Section inbuilt within the CPU. In some mobile phones,
mobile phone: these sound signals are received via coil /
resistance. Some mobile phones have audio IC in
1. Switch off the phone the audio section, while others have audio
2. Remove the battery cover amplifier.
3. Remove the battery, SIM card memory card (if any) The ringer, buzzer or speaker in most mobile
4. Remove all the screws from the phone phones are connected to the audio amplifier IC to
5. Lift back the cover with the help of a flat screwdriver Speaker/Ringer Section obtain loud sound. The amplifier IC amplifies the
6. Remove the strips (buzzer strip, display, camera, volume and speaker sound or audio signal received from the CPU of the
button strips) audio section.
7. Remove the antennae wire from the outside LED Lights are connected according to the parallel
8. Remove the motherboard and vibrator. circuit in the key backlight section. Anode ends of
Key Backlight Section all the LEDS are connected to each other and all the
To successfully disassemble a phone, you need to understand the various cathode ends to each other. 3 to 3.3 V is supplied
internal sections of a mobile phone and how they are connected to the CPU. for the functioning of these key LED Lights.
Let us look at that next.
LCD Backlight in mobile cell phones is made
according to the series circuit. A Boost Voltage
Generator section is built for the supply of high
LCD Backlight Section
voltage (10 to 18V) for the functioning of the LCD
LED. Boost coil, Boost Volt Driver IC, Rectifier Diode
are present in this section.

Positive power supply is given to this section

directly from the positive end of the battery.
Vibrator Motor Section
Negative power supply is given through a NPN
transistor or from the ground of any circuit.

Antenna, External Antenna Socket, RX-Band

Pass Filter, RF Crystal, FEM, PFO, TX-Band Pass
Network Section Filter, RF, IC, CPU are connected in the
Network Section.
 Charger and system interface connector is Mobile Phone Repair and Maintenance
made together in most modern mobile cell

Battery Charging Section

phones.
Regulator section is made separately for the
Diagnosing and Repairing Phone Faults
battery charging section. In some mobile
The correct diagnosis of mobile cell phone faults is the key to
phones, the battery charging section is made
successful and cost effective repair of the phone. Let us start by
inside the Power IC.
looking at the skills that you need to have to be able to diagnose
and repair a mobile phone.
FM Radio Driver IC, FM Antenna, Signal and
FM Radio Section Supply Components are made in the FM Radio
Section. Skills Needed to Diagnose and Repair a Mobile
Bluetooth Antenna, Bluetooth RF Signal Filter,
Phone
Bluetooth Driver IC, Supply and Signal
Components are found in this section. The Before you can diagnose and repair a phone, there are some skills
Bluetooth Section that you need to learn. These skills are:
Bluetooth section functions like the Network
• Soldering
Section. The RF-CLK signal is given to the
Bluetooth driver IC during signal processing. • Desoldering
• Testing using a multimeter
The hands free jack, hands free MIC, speaker • Jumper setting
signal component and hands free audio
Hands free (Earphone) Section:
amplifier are present in this section. Hands Soldering
free symbol is displayed after connecting the
Soldering is a process in which two or more metal items are joined
Hands free jack.
together by melting and flowing a filler metal into the joint. The filler
metal has a relatively lower melting point.

Assembling a Mobile Phone

The following are the steps that you should take when assembling a mobile phone:

1. Fix the vibrator strips of speaker and volume button

2. Fix the motherboard
3. Connect the antenna with wire
4. Place the camera and connect it
5. Place the buzzer
6. Put the camera cover Figure 27: Picture showing A technician Soldering
7. Make sure that the LCD is working before you place the screen
8. Put battery and battery cover

So far you have learnt about the hazards of mobile phone repair, the parts of a
mobile phone, the tools to use and how to assemble and disassemble a mobile Steps In Soldering
phone. This shall be followed by looking at how to diagnose and repair a
mobile phone.
1. Prepare the following materials:
• Soldering Iron,
• Solder paste
• Long Nose Pliers,
• PCB holder,
• Electronic Components (Resistors, Diode etc.)

2. Plug and pre-heat the soldering iron.

3. Heat both items at the same time by applying the soldering iron to the
 copper pad and the component lead. Mobile Phone Repair and Maintenance
4. Continue heating and apply a few millimeters of solder. Remove the iron and
allow the solder joint to cool naturally.
5. It only takes a second or two to make the perfect joint, which should appear Display
shiny.

Function and
Desoldering
Range switch
Desoldering is the removal of solder and components from a printed circuit
board for troubleshooting, repair, replacement, and salvage.

Common Jack

VΩm A jack Red Probe

Black Probe

Figure 29: Parts of a multimeter

Figure 28: Desoldering

We shall now discuss how to measure resistance, voltage and
current using a multimeter.
Steps in desoldering

1. Use a solder wick (finely braided copper) to wick away excess solder from a de- a) Measuring Resistance
soldered connection.
2. Apply the solder wick and use the soldering iron to the de-soldered To measure resistance follow these steps:
connection. The solder wick will draw the excess solder off the PCB pad. 1. Plug your red and black
probes into the appropriate
sockets on your multimeter.
Testing a phone using a multimeter 2. Choose the appropriate resistance
measurement setting
We hope you still remember that a multimeter is a device that is used to measure millimet
the voltage, current and resistance of various components of a mobile phone. Figure e
29 below shows the various parts of a multimeter 3. Hold the probes against the resistor.
4. Check the resistor value on the display.

Figure 30: Using a Multimeter

Take Note:
Always turn off the power supply to your
circuit before
measuring resistance.

b) Measuring voltage

Testing for proper supply voltage is usually the first step when
troubleshooting a circuit. To measure voltage you should follow
these steps:
 1. Select V~ (ac) or V (dc), as desired. Mobile Phone Repair and Maintenance
2. Plug the black test probe into the COM input jack. Plug the
red test probe into the V input jack.
3. If the DMM has a manual range only, select the highest
range so as not to overload the input. The Figure 31 Below shows jumper settings in of the jumpers may look like on
4. Touch the circuit with the tips of the probes your motherboard. In this example, the jumper is the white block covering two of
5. Read the number in the display window and take note of the unit the three gold pins. Also, next to the pins is a silkscreen description of what the pins
of measurement. do, in this case when pins 1-2 are jumped the computer is operating normal, when 2
3 are jumped it is set into configuration mode, and when open the computer will be
in recovery mode.
c) Measuring Current
1. Turn off power to the circuit.
2. Cut or unsolder the circuit, creating a place where the meter probes can be
inserted.
3. Select A~ (ac) or A (dc) as desired.
4. Plug the black test probe into the COM input jack. Plug the red test probe
into the amp or milliamp input jack, depending on the expected value of
the reading.
5. Connect the probe tips to the circuit across the break so that all current will
flow through the DMM (a series connection).
6. Turn the circuit power back on.

Jumper setting
Jumpering means to temporarily complete a circuit or to bypass a break in a circuit
by making a connection from one point to another. Figure 31: Jumper Setting

A good conductor wire is used to make a jumper which by-passes the

components and passes on a signal or supply line for further uses. You now know the skills that you need in order to diagnose and repair a
mobile phone. Let us now learn how to diagnose and repair mobile phones.
When wire is used as a jumper, it must have some special specifications as required.
These jumper wires can mainly be of two types i.e. insulated and non-insulated. In
the mobile phone insulated wires are used for jumpers. The length of a jumper
depends on the two points connected in between.
Mobile Phone Diagnosis
Why do Jumpering There are two methods that you can use to find out faulty or damaged
components in a mobile phone. These are:
While repairing mobile phones, we find that certain faulty components are very
• The cold testing method
difficult to get from the market. To repair such mobile phones the only immediate
• The hot testing method
option is the use of jumpers. By use of jumpers we will bypass the faulty
components specifically.

How to Jumper The Cold Testing Method:

1. Disassemble mobile phone and place it on a PCB holder.
Cold testing is when we use a multimeter to check the value of resistance at the tim
2. Using a multimeter, check track and find the fault or the missing track that of repairing a fault in a mobile phone. During cold testing do not power the phone
need jumper.
from any equipment. Use the diode range and beep sound from the multimeter to
3. Apply liquid soldering flux to the points where you need to solder find fault in the mobile phone. During cold testing, you should connect the RED
jumper wire. probe of the multimeter to the ground of the mobile phone PCB, and use the BLACK
4. Cut jumper wire to desired length and remove its lamination using blade probe to touch the testing points of the mobile phone. During the fault-finding and
cutter. repairing process of each part, component or section, you should receive the
5. Hold one end of the jumper wire and solder it to one point of the faulty following correct values:
circuit track. Use a good quality tweezers to hold the wire and good quality
of soldering iron and solder wire to solder.
1. Ear Phone Connector Tip (+ , -): .500 to .700
6. Now hold the other end of the jumper wire and solder to the other point of
the track 2. Loud Speaker / Ringer Connector Tip (+,-): .300 to .600
7. Using a multimeter check the jumper. 3. Battery Connector Tip (+): .400 to .500
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

4. Battery Connector Tip (Sense): above .800 13. Battery Charging Out Point (+,-): 3.7 to 4.2
5. Display Connector Supply Pins: .250 to .400 14. SIM Card Connector Pin 1 (VSim) when SIM Connected: 1.8 to 3.0
6. Display Connector Signal Pins: .500 to .800 15. SIM Card Connector Pin 2,3,6 when working: 0 to 2.8
7. Camera Connector Supply Pins: .250 to .400 16. Micro SD Card Connector Pin: 2.8
8. Camera Connector Signal Pins: .600 to .900 17. Micro Card Connector Pin 1,2,3,5,7,8: 0 to 2.8
9. Key Tip (Row and Column): .400 to .800 18. Data RX and TX Pins: 1.8 to 2.8
10. Charger Connector Tip: .600 to .700
11. Vibrator Motor Connector: .40 to .500
12. Power ON / OFF Switch Point (+): .600 to .900
Activity :
13. MIC Connector Tip (Analog MIC) (+,-): .700 to .900
Mobile phone diagnosis .
14. Battery Charging Out Point (+,-): .300 to .400
15. SIM Card Connector Pin 1 (VSim): .500 to .700 The following statements describe either the cold testing or hot testing methods
16. SIM Card Connector Pin 2,3,6: .400 to .800 for diagnosing mobile phone problems. Write the correct diagnosis method again
statement that best describes it.
17. SIM Card Connector Pin 4 (GND): .00 (Beep)
18. Micro SD Card Connector Pin 4: .500 to .600
Description of diagnosis method Name of Diagnosis method
19. Micro Card Connector Pin 6 (GND): .00 (Beep)
Checks the value of resistance using a multimeter
20. Micro Card Connector Pin 1,2,3,5,7,8: .600 to .800 1.
to diagnose a problem
21. RTC: .400 to .500
Checks the voltage of damaged part by giving
22. Data RX and TX Pins: .600 to .700 2. power to the mobile phone using a batter of DC
power.
3. The phone is not powered during testing
Hot Testing:
4. Fault is found by powering the mobile phone with a
The hot testing method is adopted when the fault cannot be found or when the battery
cell phone cannot be repaired using the cold testing method. In this method, the
VOLTAGE of the damaged part or component is checked. The fault is found by Compare your answer with what you read in the following section.
powering the mobile phone with a battery which has a DC power supply. Once you
power the phone, you should select the DCV (DC Volt) range of the Multimeter.
Then you should connect the BLACK probe of the Multimeter to the ground of the You now know how to diagnose a fault in a mobile phone using the hot and cold
phone’s PCB and ensure the RED Probe touches the Testing Points During hot testing, the voltage method. In the next section we shall learn about the common mobile phone fau
of different part or sections should be as follows (all values in Volt):

1. Ear Phone Connector Tip (+ , -) when working: .0 to 2.5

2. Loud Speaker / Ringer Connector Tip (+,-) when working: .0 to 2.5
3. Battery Connector Tip (+): 3.7
4. Display Connector Supply Pins: 1.8 to 2.9
5. Display Connector Signal Pins when working: .0 to 1.8
6. Camera Connector Supply Pins: 1.8 to 2.9
7. Camera Connector Signal Pins when working: .0 to 1.8
8. Key Tip (Row and Column) One Side: 1.8 to 2.8
9. Charger Connector Tip: 5 to 6
10. Vibrator Motor Connector Tip when Working: 1.9 to 3.6
11. Power ON / OFF Switch Point (+): 3 to 3.6
12. MIC Connector Tip (Analog MIC) (+,-): 1.8 to 3.0
 Mobile Phone Repair and Maintenance
Mobile Phone Repair and Maintenance

Repair of Common Faults j) Keypad problems

k) SIM faults
l) WiFi problem and internet connectivity problems

What is a fault?
a) Battery Charging Faults/Problems
A fault is a defect (a failure in a circuit) or an electronic device.
Battery charging faults manifest in a number of ways:
• The battery is not charge at all,
What causes faults or failures in mobile phones? • There is a sign of battery charging but the battery does not get charged.
• When the charger is inserted, it shows charger removed…etc
Failures can be caused by any of the following: • When the charger is connected it sh
• excess temperature, • When the charger is inserted the mobile phone gets hot.
• excess current or voltage,
• ionizing radiation, Solutions to Battery charging faults
• mechanical shock,
• stress or impact, 1. Change the charger and check. The voltage must be between 5 and 7 Volts.
• contamination, 2. Clean, resold or change the charger Connector.
• mechanical stress, 3. If the phone shows “FALSE CHARGING” t do direct charging as shown in Figur
• short circuits,
• imperfect connections, 4. If the problem is not solved then change the battery and check again
• poor insulation or wiring caused by grounding. 5. Check the voltage of the battery connector using a Multimeter. The voltage
should be between 1.5 and 3.7 Volts.
There are three types of mobile phone faults:
(i) Hardware faults: occur due to hardware malfunctioning 6. If there is no voltage in the connector check the track of the charging
section. Refer to the diagram of the particular model of the mobile phone.
(ii) Software faults: occur due to problems with software
7. If the problem still persists, check the fuse, coil and regulator one by one and
(iii) Settings faults: occur due to wrong/invalid settings
change the faulty part.
8. If the problem is still not solved then heat or change the charging IC.
Let us discuss each type of faults and how they can be repaired. 9. Finally heat, re-ball or change the Power IC.

Hardware Faults
There are many hardware faults that can occur in a mobile phone, and these may + + + -
include the following: 3.6V Zenor Diode
a) Battery charging faults/problems - Battery Connector
b) Mobile phone battery problem (faults) Charging Connector
c) Network not working problem
d) Overheating problem Figure 32: Charging the battery of a phone using a zenordiode
e) Sound faults
f) Ear piece, ringer and microphone problem
g) Display problems b) Mobile Phone Battery problem
h) Lighting or LED problems
i) Touchscreen problems A mobile cell phone can have any of the following battery problems:
• Low Battery
• Battery Drains Fast
• Battery Backup Low,
• Battery Not charging
 Mobile Phone Repair and Maintenance
Mobile Phone Repair and Maintenance

d) Network Signal and Call Drop Problem

Solutions to Battery faults If a mobile phone is having network problems and dropping calls, then
you should use the following steps to solve it:
1. Check the battery connector and charger plug to see if there is any problem.
2. Check if there is any dust or corrosion in the connector or any broken pin. 1. Check the SIM Card. Insert the SIM card in other mobile phone and see if the n
Clean the points using IPA or cleaning swabs. problem persists or problem of ‘call drop’ still exists
3. Check the Interface Connector to see if there is any dust. If there is dust 2. Alternatively, try to insert another SIM card inside the mobile phone th
clean or replace the interface connector. has the network problem.
4. If the battery problem is not solved then upgrade the software or operating 3. If the problem is caused by the SIM card, then you should change or
system to latest version replace it.
5. If the problem is still not solved then check the Mobile Phone PBA current 4. If the problem is still not resolved then upgrade the operating system to
consumption. the latest version. You can also rewrite the IMEI Number of the mobile cell
6. Check for any short circuit. phone.
7. If there is serious problem at the board level then it is better to replace the 5. If the problem is not solved then you may have to change the mobile phone.
whole Logic Board of the Mobile Cell Phone.

c) Network Not Working Problem e). Mobile Phone Overheating

The common issues related to this problem include the following: A mobile phone may overheat either inside or on the body. To solve this
• There is no network in the mobile phone problem you should proceed as follows:
• There is less or weak network signal
• Sometimes there is a signal and sometimes there is no network signal. 1. Checkif the mobilephoneoverheatswhen a particularapplicationis
running or if the overheating happens all the time.
Solutions to Network fault 2. Upgrade the mobile phone software operating system to the latest version.
This may solve the overheating problem.
1. Manually search for the network. If there is a problem with the Antenna Switch. Repair or 3. Smartphone’s overheat if too many app time. Close all the applications and tr
replace it. application at a time
2. If the network resumes after manual search but the home network cannot be 4. If overheating persists, then there is some internal hardware problem.
selected, then there is a problem with the PFO. Repair or change the PFO. Change the PCB or Logic Board to solve the heating problem.
3. If the Network gets disconnected during phone calls then you should repair
or change the Network IC.
4. Clean the antenna tips and point. f). Sound Faults
5. If the network problem persists, heat or change the 26MHz Crystal Oscillator.
6. If the problem is still not solved then heat or change the Antenna Switch. You Common types of sound faults:
can also jumper if the Antenna Switch is not available. • Earpiece or ear speaker problem
7. Heat, Change or Jumper the PFO if the problem still persists. • Mobile phone speaker problem
8. Heat, re-ball or change the Network IC. • Ringer problem
9. Heat, re-ball or change the Power IC. • Vibration problem
10. Heat, re-ball or change the CPU. • Microphone problem

i). Earpiece or Ear Speaker Problem

Take Note:
If the problem is not solved by hardware interventions,
then reload the PM File in the mobile phone using the software box.
The Earpiece or speaker is the electronic component or part that helps us to
listen to sound during a phone call. It is controlled by Audio IC or Power IC
(UEM). See Figure 27 for a picture of an ear speaker.
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

The following are the types of problems associated with the ringer:
• Ringer not working
• Low sound from the Ringer
• Sound coming from Ringer but with interruption
• Sound not clear
Figure 33: Ear speaker
How to Solve Ringer Faults
The common problems associated with the ear speaker are:
• No sound during phone call 1. Check the ringer settings in the mobile phone. Check Ringer volume and
silent mode. Adjust or change the volume and /or mode if required.
• Low sound during phone call
2. If the problem is not solved then open the mobile phone and clean the ringer
• Sound has interruptions.
point and ringer connector.
3. If the problem is not solved then check the ringer by keeping the multimeter
How to Solve Earpiece or Speaker Fault
in buzzer mode. The value must be between 8 ~ 10 Ohm. If the value is not
between 8~10 Ohm then change the Ringer.
1. Check the speaker volume during a phone call.
4. If the problem is not solved then check the track of ringer section. Do
2. If speaker volume is fine, then check the earpiece by keeping the jumper wherever required.
multimeter in buzzer mode. The value must be between 25~35 Ohm. If the 5. If the problem is not solved then check the Ringer IC. Heat or change the IC.
value is not between 25~35 Ohm then change the earpiece.
6. If the problem is not solved then heat, reball or change the UEM / Logic IC.
3. If the problemis not solvedthen checkthe CircuitTrackof the 7. If the problem is still not solved then heat, reball or change the CPU.
earpiece section. Do jumper wherever required.
4. If the problem persists heat, reball of change the UEM/Audio IC.
5. If the problem is still not solved then heat, reball or change the CPU.
Take Note:
• If there is less sound from the Ringer then change the Ringer.
• If the problem is not solved then heat or change the Ringer IC.
Take Note:
If the sound is low or not clear during a phone call,
then you should change the speaker.

iii. Vibration Problem

ii. Ringer Problem The vibrator is an electronic device that generates vibrations. It is controlled by
the Logic IC or Power IC.
A Ringer is any type of electronic component that rings or plays a loud sound. It
is also called the I.H.F Speaker, buzzer, melody, etc. Figure 28 shows a picture of The common types of faults associated with the vibrator are:
a ringer. • Vibrator not working
• Vibration has an interruption
• Vibration Hangs.

How to solve Mobile Vibrator faults

1. Check the Vibrator settings in the mobile phone. Check if the Vibrator
ON or OFF.
2. If the problem is not solved then open the mobile cell phone and clean
the vibrator tips and connector.
3. If the problem is not solved then check the vibrator with the multimeter in
Buzzer Mode. The value must be between 8~16 Ohm. If the value is not
between 8~16 Ohm then change the Vibrator or Motor.
4. If the problem is not solved then check the track of the vibrator section. Do
jumper wherever required.
Figure 34: Cell phone ringers
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance
5. If the problem is not solved then heat, reball or change the UEM/Logic IC
/Power IC.
6. If the problem is still not solved then heat, reball or change the CPU. • Display is upside down.
• Display is broken.
iv. Microphone Problem • When the mobile phone is switched ON, the Logo appears and then the
display disappears
The Microphone is an electronic component that helps to transmit sound during
phone call. A microphone is controlled by Audio IC or Power IC (UEM). How to Solve Display Faults in a Mobile Cell Phone

The common types of problems associated with the microphone are: 1. Clean the display tips and display connector.
• Low sound during phone call 2. Resold the display connector
• Sound has interruption 3. Change the display
• Change in sound. 4. Check the display Track.
5. Resold or change the display IC.
How to Solve Microphone Fault 6. Heat, reball or change the CPU.

1. Check the Microphone settings.

Take Note:
• In the slider mobile phone handset, the display problem is
mainly due to a faulty display track. Change the track to solve
the problem.
• If the Display is upside down, broken or it displays information
Figure 35: Jumper Setting For Microphone on half the screen then you should change the display
• If the Display is white even after changing it, then you should
reload the software.
2. If all the settings are normal, then check and clean the Microphone tips and
connector.
3. If the problem is not solved then check the Microphone with the multimeter in
Buzzer Mode. The value must be between 600~1800 Ohm. If the value is not
in between that range, then change the Microphone. Note that only one side h) Mobile Light or LED Problem and Solution
will give a value.
4. If the problem is not solved then check the track of the Microphone section. Do The LED is the electronic component that generates light in the mobile phone. There
Jumper wherever required. are 2 types of connections in the light section of a mobile phone:
5. If the problem is not solved then heat or change the Microphone IC. • Series Connection;
6. If the problem is not solved then heat, reball, or change the UEM / Audio IC • Parallel Connection.
/Power IC.
7. If the problem is still not solved then heat, reball or change the CPU. Figure 36 shows a diagram of series and parallel connections.

g) Display Not Working

This is the part that displays information in a mobile phone. It is controlled by

the CPU. In some cell phones there is an Interface IC called the Display IC Series Connection Parallel Connection
situated between the Display and the CPU.

The following are the common types of problems associated with the display: Figure 36: Diagram Showing Series and Parallel Connections
• Display is blank.
• Display not working properly. The common symptoms of LED problems are:
• Only half the display works. • No Light.
• White display. • Light only in the Keypad or Display.
• Some lights not working
 Mobile Phone Repair and Maintenance

How to Solve a LED problem

1. Check the light settings.

2. If the settings are normal then resold all the LED.
3. If the problem is not solved then change the display or the screen.
4. Next check all the LEDs with the multimeter on Buzzer mode. If the LED is
good then it will glow. If the LED is faulty then it will not glow.
5. Change the LED or jumper if required.
6. If the problem is not solved then check the Track of the light section of the
PCB and jumper if required.
7. Next check the Boosting Coil and change if required.
8. If the problem is not solved then heat or change the Light IC.
9. If the problem is still not solved then heat, reball or change the Power IC.

i) Phone Touch Screen (PDA) fault

A Touch Screen (PDA) is an electronic component that allows you to input data
or control your mobile phone by touching the screen. It normally has 4 Points
namely:
• (+),
• (-),
• (RX),
• (TX).

The touch screen is normally controlled by the CPU. In some mobile

phones there is an Interface IC called PDA IC or Screen Touch IC.

The following are the faults associated with the Touch Screen
• Touch Screen not working.
• Only half the Touch Screen works.
• When one key is pressed another key works.

How to Solve Touch Screen (PDA) Faults

1. Check the settings if the mobile phone has both a keypad and a
touch screen.
2. Clean and resold the PDA Tips and PDA connector.
3. Change the PDA.
4. Check the Track of the PDA section and Jumper if required.
5. Heat or change the PDA IC
6. Heat, reball or change the CPU
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

Take Note:
Take Note:
• If the PDA problem is not solved by hardware solutions, then reload the
software to solve the problem. • If you press a key and it takes a long time to work, then you
should reload the software to solve this problem.
• Any PDA of the same size will fit in any mobile phone. Any one of the 5 Jumper
Settings shown in figure 37 below will work: • In all Nokia mobile phones, if none or only a few keys are
working, then you should change the keypad IC to solve
the problem.

(i) Mobile Phone SIM faults

A Subscriber Identify Module (SIM) card is an integrated circuit that securely

stores information about the number of the cell phone line, password, and
information related to your local network service. It has a unique serial
5 Types of PDA jumper solution
number.
Figure 37: Jumper settings for PDA
The following are the common problems associated with the SIM card:
• SIM is inserted but still there is an error message
(h) Keypad Problems • The mobile phone goes OFFLINE when the SIM card is inserted.
• The SIM works for sometime and then stops working.
The keypad enables you to enter data, such as, phone numbers and names in your mobile • There is a message that says “Invalid Sim card”
phone.
How to Solve SIM Card Fault
The main types of problems associated with the keypad are:
• Some keys not working.
1. Check settings and see if the mobile phone is in Flight Mode.
• Keys need more pressure to work. If it is in “ Flight Mode” then change it to Normal mode.
• When a key is pressed it works continuously.
2. Clean the SIM Card Tips and SIM Connector.
• When one key is pressed, some other key works
• When one key is pressed, some other key works simultaneously. 3. If the problem is not solved then change the SIM card and check.
4. If the problem still persists then change the SIM connector.
How to Solve a Keypad Faults 5. If you still do not find a solution to the problem, check the Track of the SIM
section.
1. Check the facial of the keypad. 6. If the problem is still not solved then heat or change the SIM IC.
2. Clean the keypad and keypad points shown in Figure 38 below.
7. Finally, if there is no change, heat, reball or change the Power IC.

Row
Column

Figure 38: Keypads and keypad points

3. Using the multimeter in Buzzer Mode and check the Row and Column of the Keypad. If
there is a beeping sound then the keypad is working.
4. If there is no improvement, heat or change the Keypad IC or the Interface IC.
5. If still no change, heat, reball or change the CPU.
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

Software Faults
A software is a set of programs, routines and symbolic language that control
Take Note: the functions of hardware and directs its operations.
• Check if the IMEI number is good or is corrupt by dialling the
number, *#06#. If the response reads as follows: The common software problems are:
35826********220 OR *************??? OR • Display problems
************000? OR ***************? • No signal message
Then the IMEI number is corrupt. • Dead phone set
• Reload the IMEI Number to solve the SIM Problem. • Phone on test mode
• Check the BSI Point of the battery. The middle Pin is the BSI Phone not charging
point. Change the battery and check. If the display shows • Phone has message to contact service provider
“Not Charging” and at the problem, then it could be either • Phone hangs, goes off, freezes or has slow processing
due to a BSI Problem of the Battery or the BSI Track of the
PCB. How to solve these problem:
• If you need to change the SIM IC and the SIM IC is not
available then you can do Jumper. The function of the SIM IC 1. Check the downloaded applications and note when the problem happened.
is just to complete the circuit. 2. Note whether the problem is happening when a certain application
is running.
3. Remove the application that is causing the problem
4. If the problem is still not solved then reset the factory settings of the
mobile phone and update the software.
(j) Mobile Wi-Fi Wireless Internet Connection Problem:
You have now come to the end of our topic on common mobile phone problems
This problem may present in the following ways: or faults. Before you move on, do the following activity to evaluate your
• No internet understanding of this section.
• Low Wi-Fi signal
• Wi-Fi cannot be enabled

How to Solve Wi-Fi problem Activity 7:

Common mobile phone faults and their solutions. (4 minutes).
1. Enable Wi-Fi and check if it is working or not. Make sure you are connected
to a wireless network. Make sure the password is correct. Match the cell phone problems or fault in Column A with the correct solutions in
2. If the Wi-Fi cannot be enabled and you are not able to use or access the Column B.
internet, then there could be problem with the mobile phone PCB and you
may have to replace it. Column A Column B
3. If the Wi-Fi can be enabled then there is no problem with the PCB. Just Cell Phone Problem Solutions
upgrade the software of the mobile phone to the latest version. Display not working Clean and resolder the PDA tips
Faulty ear piece Check the speaker volume
You now know the common hardware problems found in mobile cell phones. Next Close all the applications and run one
let us discuss the software problems and how to solve them. Phone is overheating
at a time
Network problem Change the charger
Vibrator is not working Repair the antenna
Phone dropping calls Rewrite the IMEI number of the phone
Touch screen problem Check if phone is in vibrate mode
Battery problem Resold the display connector

Compare your answers with those given at the end of this course.
 Mobile Phone Repair and Maintenance
Glossary
Congratulations! You have come to the end of our course on mobile phone repair Anything that has potential to cause harm to yourself and all
and maintenance. Let us review what you have learnt. Hazard
those around you.
A fault A defect (a failure in a circuit) of an electronic component
An electrical component that can break an electrical circuit,
Summary Switch thereby interrupting the current or diverting it from one
conductor to another.
The hazards included: burns, pricks, environmental pollution and falls. We also Jumper Jumpers are small blocks on a circuit board with two or more
discussed the factors to consider when selecting tools for mobile phone repair. pins emerging from them.
These factors included cost, suitability and quality of the tools. In addition, we Boot To start or restart a mobile device.
examined the tools used for mobile phone repair, such as solder wire, PCB holder,
Bluetooth A wireless technology standard for exchanging data over
jump wire, and screw driver. Next we determined the steps that you should follow
short distances
to disassemble and assemble a mobile phone and how to diagnose mobile phone
faults. Lastly, we discussed common hardware and software faults and how to solve Driver A program that operates or controls a particular type of
them. device.
The main board that holds electronic components of the
Motherboard system,(CPU) and memory, and provides connectors for
other peripherals.
To identify the nature of a problem by examining the
Diagnose
symptoms.
A process in which two or more metal items are joined
Soldering together by melting and flowing a filler metal (solder) into
the joint. The filler metal has a lower melting point than the
adjoining metal.
A tool normally used for applying heat to two or more
Soldering Iron adjoining metal parts in order for the solder to melt and bind
them securely and conductively.
A fusible metal alloy with a melting point or melting range of
Solder 90 to 450 degree Celsius, used in a process called soldering
where it is melted to join metallic surfaces.
Disassemble To take something apart; or to disconnect the pieces of
something.
Assemble
To bring things together for a common purpose.
The difference in charge between two points or amount of
Voltage potential energy between two points Voltage is measured in
volts which uses the symbol V.
How much electricity is flowing through the circuit. A current
Current is measured in amperes. The symbol for amperes or amps in
short is described by the symbol A.
Resistance How difficult it is for electricity to flow through something.
Resistance is measured in ohms.
A process where the defective chip is lifted off and repaired
by applying lead based solder on the chip and placing it back
Reballing on the board or replacing the component with a new one
while also applying lead based solder on it before soldering it
back on the circuit board.
 Mobile Phone Repair and Maintenance

References
Wikipedia. 2010.
Form factor (mobile phones)
. [ONLINE] Available at:
https://en.wikipedia.org/wiki/Form_factor_%28mobile_phones%29. [Accessed
04 July 15].

Shashilata D. 2012.
mobile-phone-repairing-tools-equipment-tools-to-repair-mobile-
cell-phone.html
. [ONLINE] Available at:
http://www.mobilecellphonerepairing.com.
[Accessed 05 February 15].

Service manuals, SchematicsService

. 2010. manuals, Schematics > Mobile Phones >
Nokia. [ONLINE] Available at:
http://www.s-manuals.com/phone/nokia. [Accessed 05 February 15].

Phone Repair Tutorials.2011.

Free CellPhone Repair Tutorials
[ONLINE] Available at:
http://cellphonerepairtutorials.blogspot.com.[Accessed 05 February 15].

computer hope.2011.
What is a Jumper?
.[ONLINE] Available at:
http://www.computerhope.com/jargon/j/jumper.htm.[Accessed 06 March 15].

allgsmtips. 2013.
What Are The Parts Inside A Cell
. [ONLINE]
Phone Available at:
http://allgsmtips.com/. [Accessed 06 February 15].
 Mobile Phone Repair and Maintenance Mobile Phone Repair and Maintenance

Hardware Faults 7. State any six types of SIM faults

(i)
1. Name any five types of hardware faults (ii)
(i) (iii)
(ii) (iv)
(iii) (v)
(iv) (vi)
(v)
8. Name any six Micro SD Card /MMC faults
(i)
2. List four types of battery faults. (ii)
(i) (iii)
(ii) (iv)
(iii) (v)
(iv) (vi)

9 Complete the table below by writing the possible causes of the phone faults i
3. List three types of signal faults /Network faults left hand column.
(i)
(ii) No: Phone problem Possible cause
(iii)
1. Unable to send SMS
2. Only incoming call
4. Identify four types of sound faults? 3. Security code
(i) 4. No signal
(ii) 5. SIM locked message
(iii) 6. Contact service provider
(iv)

5. State three types of display faults

(i)
(ii) Software Faults
(iii)
10. List any five phone software faults.
(i)
6. State any five types of keypad faults (ii)
(i) (iii)
(ii) (iv)
(iii) (v)
(iv)
(v)