USE MULTIMETER IN MOBILE PHONE REPAIR

USE MULTIMETER IN MOBILE PHONE REPAIR

Learn how to use a multimeter in mobile phone repairs by reading this short guide.

A multimeter is used for testing and to check readings of various parts and components in a mobile phone.

There are two types of multimeters available in the market. They are:

Digital Multimeter

Analog Multimeter

You can use any type of the ones mentioned above as both of them will do the same thing.

The only difference is that a digital one will show you the readings in digital format thereby saving you time and effort. While in an analog one, you will have to see the reading as per the arrow on its screen.

Most technicians prefer to use the digital models. The analog models are used by old generation technicians, as they love and have a distinct affinity to them!

A multimeter whether digital or analog has two wires (also called probes), a red and a black wire. The red probe is positive (+), while the black probe is negative(-). In electronics, always red is positive and black is negative.

When you buy a new multimeter, insert one end of the red probe in VΩ slot (round hole), and the black probe in the COM (means common) slot. The 3rd slot i.e 10A or 20A is not used in cell phone repairs.

In mobile phone repairs, we use only any 1 of the below given settings in multimeter:

1. DC Volt Setting: We use this setting to check the voltages of the things to be checked. In DC volt setting the output voltage of various things like battery, battery connector, charger, charging
connector, etc. can be checked. It is indicated by a capital V and straight line with 3 dots below it.

2.  Resistance Setting:  By this meter, the resistance of various parts like resistors, etc can be checked. We can also check resistance between 2 points if it is instructed to check in a service manual to check it to get a particular reading while repairing a fault in the motherboard. We can also check the microphone of cell phone with this setting.

3.  Continuity:  This is also called diode setting. When you touch the red and the black probe ends while on this setting, you will be able to hear a beep sound. By keeping the multimeter on this setting, we can check the continuity between the given 2 points. We can check whether the tracks are open or not. If the multimeter shows continuity, it will give a beep sound. That will mean that the track is ok. And if it does not beep, it will mean that the track is broken.

To repair a broken track, all technicians make jumpers. Jumpering means soldering a thin insulated wire from one end of a broken track to the other end.

With this setting, we also check whether the circuit board is short or not. We check the shorting by keeping the wires on the positive and negative terminals of the battery connector and also reverse the wires. If we get beep sound both ways then the circuit board is short, if we get beep sound only once then it is not short.

In some phone models you will not hear the beep sound. Instead you will either see some reading (like 255, 282, etc) on the screen of the multimeter or just 1. So if you see reading 2 times i.e even after reversing the probes, then the circuit board is short. You should get reading one time and just 1 on the other time.

We can also check speaker and ringer by continuity.

How To Test LCD of A Cell Phone

It is not difficult to check LCD (Display) of a cell phone or a tablet. LCDs being delicate tend to crack, leave blots or simply sop working. So if its is broken or cracked, you can see its broken manually. Even if there is a blot on it, you can see it physically. But what if its looking good and still there is no graphics on the display? The problem may be either the LCD is faulty or there is some problem in the PCB.

So how do we test it?

A faulty LCD can be of the following types:

Cracked or broken

A blot (round in shape which will spread rapidly!)

Blank display with no graphics.

An LCD with just graphics and no light (LED) glowing on it.

You can check LCD of a cell phone by any of the below methods

1. LCD Testers: There are testing machines available in the market for checking of LCDs. The problem here is that as all models have different LCDs, you will need to buy an LCD tester machine for all types and models and will run into hundreds! As all LCDs of smartphones,  be it an iPhone or a Samsung Galaxy or an Xperia have different size connectors, with varying no of connecting pins, a universal LCD checking machine cannot be made. This is a major constraint and hence not at all feasible unless you deal in repairs or testing of thousands of units of a particular model.

2. Check it in same model cell phone: The second option is if you have a working handset of the same model, you can easily put your LCD into that handset and check if its working or not. For eg. If you want to check the LCD of your iPhone 5s, you can check it in a working iPhone 5s. So what if you do not have a working handset of the same model. Read the last option!

3. Check with a new LCD: Replace your LCD with a new one. If graphics appear on the LCD, that will mean your old LCD is faulty. And if the new LCD also is not displaying graphics, it will mean your old LCD may be ok. And the problem may be in the PCB. The problem may be in the LCD connector, its connections, PCB or an IC controlling the display function.

Note:

1. You cannot check LCD with a multimeter or an oscilloscope!

2. In Samsung phones, you can also check clarity of the screen with the code *#0*#. You can check red, green and blue colours with this code.

3. As regards to being original or duplicate, its better to buy them from good and reputed vendors. Again, if you have many LCDs, you can switch on the handset and compare the clarity with various LCDs yourself.

4. If no light (LED) is glowing, please check LCD brightness settings first before opening your mobile phone.

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How to Check Shorting In Mobile Phone

The first thing you have to check in dead mobile phones after checking the battery is shorting. And if it is short, you will first have to remove it to get it repaired.

All technicians should know how to remove a short circuit in cell phones.

Reasons for shorting in mobile phones:

*Phone falling in water. This is the most common reason

*Handset overheating.

*Using an incompatible or faulty charger for charging

*Sometimes, sparks or smoke coming out of the handset due to any reason.

We have to understand the below 2 terms of electronics to understand shorting better:

Open circuit: If a track is broken, then it is said that the track is open.

Short circuit: If 2 parallel separate tracks touch each other due to some fault, it is called short circuit.

Note: In circuit boards of cell phones, tablets or any other electronic device, there are tracks instead of wires through which current flows. Hence we use the term ‘tracks’ instead of wires or cables.

Option 1.

 How to check shorting in mobile phones with multimeter:

 We can easily check whether there is shorting in the circuit board or not with the help of a multimeter.

Follow the steps below:

Keep the multimeter on continuity setting (Also called diode setting)

Identify the positive and negative terminals of the battery connector. The positive terminal (+) is the pin of the battery connector where the positive terminal of the battery touches on it. It is also called vBat (Battery Voltage) pin. While negative terminal (-) is the pin of the battery connector where the negative terminal of the battery touches on it. It is also called GND (Ground) pin.

Now touch the red probe (+) of the multimeter to negative terminal of the battery connector.

If you see any reading on the multimeter or hear a continuous beep sound, then the motherboard is short i.e your mobile phone is short. And if there is no reading or no continuous beep sound, the board is not short. If you are using an analogue multimeter, keep it on Ohms(x10) setting. If the pointer (needle) moves even a little, than it is short, otherwise, it’s okay.

Option 2.

 How to check shorting in mobile phones with DC Power Supply:

A DC Supply is also called jhatka machine or battery eliminator. Its work is to convert AC voltage coming from an AC volt source to DC voltage. To check shorting, follow the step below:

Switch on the DC power supply. Now select the output voltage as much as its battery voltage. You can read it on the battery. In most phones, it is 3.7v or 3.8v. Some Chinese phones have output of 4.2 volt.

Connect red probe to the positive terminal of the battery connector (vBat pin) and the black probe to the negative terminal (GND)as well as the 3rd pin called BSI. And do not touch any other key or button.

Now, if you see any amount of current on the screen, then it means, the circuit board is short.

And if, there is the screen shows ‘0.00’ in the current reading, then it is okay.

Problems in handset if it is short:

*Dead
*Battery drains and discharges fast
*Overheating
*Hanging
*Switches off automatically or restarts.

*If the circuit board is short, you will first have to remove shorting for fixing the problem, especially, if the handset is in dead condition.

Note: The above procedure to check shorting is the same for all brands of cell phones and tablets including Samsung, iPhone, Nokia, Sony, HTC, Motorola and Chinese handsets. It will be the same for all smartphones be it based on iOS, android or Windows OS.
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REMOVE SHORTING IN MOBILE PHONE
If your mobile phone is short, it can have various problems like it may not power on (dead), it may overheat (although it is normal in some models!), its battery may drain and discharge very fast, it may hang and freeze frequently, it may restart sometimes, etc. It is called short-circuit.

Before removing shorting you should know whether your handset’s circuit board is short or not. Learn how to check shorting in mobile phones.

Reasons for shorting in circuit boar of mobile phones:

The most common reason is phone drenched or fallen in water.

Handset overheating.

Trying to use an incompatible or faulty charger for charging

Sparks or smoke coming out of the handset due to any reason.

To repair a short cell phone, you will have to first remove its shorting to fix it. You have to follow the procedure to remove it especially in dead handsets.

Procedure To Remove Shorting In Mobile Phones:

1. Dismantle your phone and get out the printed circuit board (PCB). Be careful, so that you do not damage it! Now remove LCD, camera, etc because we just need the board.

2. Clean the entire PCB thoroughly with any circuit cleaner like spirit, alcohol, thinner, IPA, etc. Now dry it completely. After each step, you have to check if shorting is gone or not. If not, proceed to the next step.

3. Now try to deep clean the PCB. There is a liquid called Elma used by watch repair technicians in the eastern countries named Elma. If you do not have access to Elma solution, you can use a solution of any mild soap like Jif.

Elma procedure: Dip the PCB in Elma or a mild soap solution for 2 to 4 hours. Remove the PCB and clean it thoroughly with a brush. Dry the PCB completely so that not even a droplet of water or soap solution remains. For drying, you can use a hair dryer, over a flame or even direct sunlight although a hair dryer is a preferable option.

Precautions: Make sure you remove the LCD, camera, etc from the PCB before dipping the circuit in Elma. Also make sure, you have dried the PCB completely. It’s advisable to dry the PCB twice as water droplets remain below the chips on the motherboard.

Alternate method: You can also use an ultrasonic cleaner to do the above procedure. The advantage is that you do not have to wait for 2 to 4 hours. Instead you will finish the entire procedure in less than 15 minutes. Learn how to use ultrasonic cleaner machine in mobile phone repairs. 

If shorting goes, you may think there was some dust particle, which lead to shorting. Always consider dust to be one of the worst enemy for a smoothly working circuit board. The other enemy is moisture. If the motherboard is still short, luck is not on your side. You will have to follow advanced procedure. Follow the step below:

There are two things we should consider:

A component or IC on the PCB is short and making the entire PCB short.

The entire PCB is short

So, if the PCB is short, we cannot dig it out and fix it! We will consider that any of the component or IC is short.

Manually inspect if any component like resistor, capacitor, diode, etc is short. There are more chances of capacitors being short. They would look a little more dark or black in colour because of getting burnt. Remove it and then check shorting with a multimeter. If it is gone, you have to solder a same, working component in its place. If still the problem is not solved, proceed further.

Connect the PCB to its battery, press the power button and keep it in this position for 10-20 seconds. Remove the battery and immediately check if any component or IC is heating. The part which is heating is most likely short. Remove it and check again. If the problem goes, replace the heating component / IC.

If still there is problem then it is very difficult to repair. You will have to remove all the components one by one and check if shorting has gone or not. The part after removing which, the problem goes, is short. But this procedure is too lengthy as there are hundreds of such small components and may take days or weeks and so it is not feasible! This was only for enthusiasts or stubborn technicians who want results anyhow! So do not go for it. There comes a stage when the mother board is beyond repair i.e it cannot be repaired. If it is possible, you will have to simply replace it.

Note: The above procedure will be the same for all brands of cell phones and tablets including Samsung, iPhone, Nokia, Sony, HTC, LG, Motorola and Chinese handsets. It will be the same for all smartphones be it based on iOS, android or Windows OS.
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How To Format a Mobile Phone
Formatting a cell phone means erasing or deleting all the stored data and information like contacts, images, multimedia files, etc from the phone memory, this DOES NOT include the data you may have stored in the MMC (memory card) or memory chip you have inserted in you phone, in other words data stored in your memory card is not deleted and will remain safe.

In formatting your cell phone your operating system like iOS, symbian, Windows or Android are not at all to be reinstalled unlike in computers. The OS is not affected and it remains intact.

The procedure where you have to reinstall the OS is called flashing in cell phone repair jargon, which is very much different from formatting. So let us go ahead with formatting a phone and not get confused with flashing. DIY type of people especially get confused between these two terms.

In general the process of formatting is usually done when there is any problem due to infection by a virus.

The most common signs of virus infected phone are:

Opening of an application takes time or in other words the process is very slow.

The phone switches off and restarts on its own frequently.

The phone hangs up i.e freezes often ie to say no buttons operate and the screen remains as it is.

Sometimes some application and/or files get corrupt or they are inaccessible.

Any related problem that looks like the system is infected by virus.

The method to format a cell phone is given below:

Open the menu and select settings. You will find an option for reset settings in this menu. Select this. In this you will get multiple options viz. 1. reset settings only and 2. Reset all / master reset / erase all data. Select the second one. You will be asked for the security code, If you have changed the default code then type the changed code if not then enter the default security code . If you do not know the default code then click on defauly security code on main page  and get the code for your brand of mobile from there and type in. Your phone will be formatted.

The above procedure has deleted data from phone memory only. It is necessary to know that whenever the phone is infected, the virus infects the internal memory as well as the MMC (memory card). Hence you will have to format the memory card or scan it with an antivirus.
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DEFAULT SECURITY CODE

All cellphones that are manufactured always come with a factory set security code, this is for security purpose to protect the information and data stored in the phone by the user. These codes are constant for all models of phone with their respective manufacturers. Whenever you intend to make any changes in the security settings you are asked to input this very code as specified by the brand unless you have changed this code to as per your convenience. Security codes are used for different functions say for instance to unlock your keypad or while rebooting ie switching on you phone or to restore the phone to its original factory settings etc. It is sometimes also needed when you want to perform a soft-reset or reset your phone to its original factory settings.

If perchance you input the code as per specified by the particular brand of the manufacturer and a message displayed on the screen reads as ‘WRONG CODE’ or ‘CODE ERROR’ it is deduced that the code has been changed or tampered with maybe by your friend or could be by your child, otherwise the default code will never fail you.

We on our part would advise you to always change these factory set codes for your own security to protect all your data and information, but also remind you to remember this code and do not forget it. If it so happens and you type a wrong code then the phone gets locked and you may need professional help to get it unlocked and restarted again.

The default codes of the various brands having any OS like iOS, Windows, Android, Asha or Symbian have the same code as that of its manufacturer and are listed below and are constant for all their models.

These are factory set codes which will always work. We have listed more than one code for some so try any one of these and we assure you they will help you out.

DEFAULT ORIGINAL FACTORY SECURITY CODES:

NOKIA :  12345

SAMSUNG :  0000  (4 times zero)   or

000000 (6 times zero)  or

00000000 ( 8 times zero)

CHINA MOBILES / CHINESE BRANDS:  0000   or  1122   or  1234

ALL OTHER BRANDS
OF CELLPHONES (SONY, LG, MOTOROLA, ETC):      0000   or  1234

LAVA                           :      4321
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COMMON PHONE PROBLEM
A cell phone can get various faults and problems when using it.  So cell phone repair technicians should know what are all the faults they have to repair and fix when they open a repair center.They should know how to diagnose and troubleshoot them easily.

Basically there are 3 types of faults in cell phones

Settings Faults

Software Faults

Hardware Faults

The list of all faults in cell phone are:

1. Dead: If a phone doesn’t switch-on, it is called a dead phone.

2. Insert Sim Card: In this fault, the SIM card does not get detected.

3. Hanging Problem: In this fault, the handset freezes frequently. 

4. Network Problem: No signal and network or low network

5. Microphone Problem: No out-going sound.

6. Ringer Problem: No ring tone, music and loud speaker will not work.

7. Speaker Problem: No incoming sound.

8. Vibrator Problem: No vibration.

9. Display Problem: No graphics on LCD or broken LCD.

10. Auto Switch Off: Phone switches off automatically even if not switched-off.

11. Restart Problem: Phone restarts automatically.

12. Call Cut Off: Call gets disconnected or cuts off.

13. Charging Problem: No charging or very slow charging.

14. Keypad Problem: Keypad doesn’t work or some keys do not function. Home button or volume buttons do not work.

15: Touch Problem: Touch doesn’t work or slow touch.

16. Battery Discharge Problem: Battery gets drained very fast even when fully charged.

17. Bluetooth  Problem: Bluetooth does not work.

18. Camera  Problem: Camera does not work.

19. FM Radio: Radio does not work or no tuning.

20. LED Problem: Not light on LCD.

21.  Memory Card Problem: MMC does not get detected.

22. No Internet

23 WiFi Problem: WiFi does not function

These are the most common faults that arise in cell phones as well as smartphones and tablets. Sometimes unlocking is required if your device is locked. There are many more strange problems other than the ones mentioned above. Some of these are easy to repair while others are difficult and sometimes are beyond repair.
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How to check Smartphone Loud Speaker

A ringer, also called a loud speaker is a speaker through which you hear ringtone and music. During a call, when you activate the loud speaker, the louder voice which you start hearing also comes from the ringer. It is also called a buzzer in basic low-end mobile phones. Its work is to convert electrical signal into sound.

If the ringer becomes faulty, you will not be able to below 3 sounds:

Ringtone

Music

Loud speaker’s voice during a call

To avoid missing calls, you can switch on the vibration as a temporary solution! The method to check it will be the same for any brand or model of a mobile phone or a tablet be it an iPhone, a Samsung Galaxy, a Sony Xperia or a Nokia.

Steps to check ringer of a cell phone

Turn off your cell phone and dismantle it carefully. If you do not know how to dismantle your handset, you can watch videos of its disassembly procedure on Youtube!

Now remove the ringer carefully. It can be located anywhere inside the casing. The best way to locate it is – it will be below the opening (hole) in the casing from where you hear music! Do not misunderstand and remove the speaker by mistake. The speaker is meant to hear the calling person’s voice during a call and is a different spare part.

Now keep the multimeter on continuity setting. On this setting when you touch the tip of the red and black probes to each other, you will be able to hear a beep sound.

Now touch the tip of the 2 probes of the multimeter (the red and the black wires) to the 2 terminals (pins) of the ringer. Now if you hear a beep sound, then your ringer is good and working. And if you do not hear any beep sound, then your ringer is faulty.

Second method to check loud speaker

The other option to check or test a loud speaker of a mobile phone or a tablet is to put it in any other same working model (or a handset with the same size speaker) and check if its working properly in it. If its not working, its faulty. It’s as simple as that! In some models, the ringer comes as an entire unit. In such cases, you will have to replace the entire unit.

Note: If your ringer is ok and still you are unable to hear ringtone during a call and music as well, then check if it is connecting properly with the PCB. Clean its contact points on the PCB (Printed Circuit Board) with an eraser. If the ringer is soldered, you will have to check if its soldered properly. If its not, resolder it properly. Also try replacing with a new one. Still if the fault doesn’t go, there may be a complicated hardware problem in the PCB. It will either be due to a broken track supplying voltage to the ringer or a faulty IC. You will have to repair it by following schematic diagrams. Always check the ringer settings whether its not kept on mute before opening your handset.