Troubleshooting Mobile Phone Faults Part2

Dead Set Repairing:

We are going to discuss here some techniques and steps to repair dead condition in mobile phones irrespectively of brands in a primary way.

Key Components and functions:

* Battery* Power Switch* battery terminal* Power IC* Oscillator* Frequency divider* CPU* Flash (ROM / EEPROM)

Battery:

A battery is used to provide power supply to our mother board unit so if this battery or on of its functions fails the whole mobile phone fails to power on. So battery must be in good condition to make a mobile phone power on. Some times the third Pin used in battery which is called “BSI” is not working correctly but voltage can be found in ” + ” and ” – ” terminals, in this situation mobile phone cannot turn on.

Power Switch:

A power switch is used in a mobile phone to turn on and off mobile phones if it is faulty the whole unit cannot power on so keep checking its terminals whether they are connected with the power IC of not if not then you can make a jumper and connect it.

Battery terminal:

battery terminals connect battery to mobile phone component unit if its points are dry soldered of unsoldered or bended then you can change and fix this problem which is always in the result of no power on. so if battery terminals are working correctly you need to proceed further.

Power IC:

A power IC distributes current among all the components actually a power IC works as ” voltage regulator” and ” power on function” so if a power on function is faulty the whole unit will not power on. but there are some problems with ICs that we cannot check them whether they are working right or not rather we can only assume that they are faulty if the other functions are correct.

Oscillator:

An oscillator makes low frequency which is called clock frequency. this frequency is used to run digital components if this frequency is not available digital components fail to work and the result is power on failure. the out put frequency is used in mobile phone’s CPU and Memory chips and UEM Ic if used.

Frequency divider:

Frequency dividing is a function which is used in mobile phones to divide clocked frequency to get accurate frequency to run digital components so if divider is failed power on fault mat occur. this frequency dividing function is built in radio ICs commonly like hagar IC or Mojoelner in Nokia mobile phones.

CPU:

A CPU (central processing unit) is like a brain in mobile phones which controls the major parts of mobile phones so its functionality is very necessary in mobile phones while testing in boot process but its functionality is associated with Memory chips used in mobile phone specially Flash chip.

Flash Chip ( EEPROM)

A flash chip holds booting information in it self it has instructions stored in itself for the CPU to control other components so if flash chip or its software is damaged it mean the set do not power on. in case of damaged software the phone should be treated in flashing process.

* The word flashing denotes in mobile phones that some software installation.

Steps in Repairing Dead Sets:

Note: Some steps which cannot be take in an average mobile phone lab are avoided to be explained because oscillator and divider’s functionality can be checked by Oscilloscope which is not available in an common mobile phone lab.

How a mobile phone powers on:

First of all look at the picture below carefully. This picture describe booting detail about NOKIA mobile phones but same structure can be applied to the other brands with a little modification.

In the picture above all of you can see a little block diagram illustrating mobile phone booting sequence. first of all I am starting explanation from power switch.

When a power switch is pressed it turns on a circuit inside the power IC and this IC starts distributing power supply to other parts of mobile phones. On the first place VCO( voltage controlled oscillator) or an other type of clock oscillator starts producing a clock frequency of 26MHz in some mobile phones this clock frequency is directly used to run CPU but most of the sets in NOKIA brands it is distributed bye hagar IC or RF Signal processor and it becomes 13MHz in the end of the division process. this low frequency clock signal is used to start CPU functions now CPU which is like the brain of the mobile phone comes to the senses and first of all contacts its memory to know what are the instructions written it for this event and its memory tells CPU that if you feel that you are finding 13 MHz from hagar IC you have to run a booting test. in this test CPU tests most of the mobile phones function if they are correct CPU will order power IC to continue providing power to other parts and CPU also starts its display section. so this is the total process in which a mobile phone comes to the power on state.

Responsible parts for mobile phone power failure there are eight elements which can affect mobile phone power on function:

* Power Swicth* Battery* Battery terminal* power supply tracks* power IC* Ocsilator (VCO)

* hagar IC* flash (programming)

So we can say that when ever a mobile phone fails to power on there may be a fault in such type of parts which are used in mobile phone booting process.

How to handle water damage phones:

Ever dropped your cell phone in the sink,? Did you ever leave it in your pocket and run it through the washer? It usually means you have to replace your phone, but sometimes if you’re fast you can save the phone.

1. Remove the Battery. This is one of the most important steps. Don’t take time to think about it, electricity and water do not mix. Cutting power to your phone is a crucial first step in saving it.

2. Dry your Phone. Obviously you need to remove as much of the water as soon as you can to prevent it from getting into the phone. Use a towel or a paper towel to remove as much of the water as possible.

3. Soak in Alcohol. Alcohol is hygroscopic (attracts water), it will dissolve all the water in the phone, which will then pour out of the phone with the alcohol. Any remaining alcohol will evaporate. Alcohol will not harm your phone but may mess up glue (from stickers and the like). Use 95% alcohol, not the regular 70% rubbing type. Do it outside!. If you use alcohol, do not follow the rest of the advice here, instead leave your phone outside for a day or two to dry.

4. Allow the phone to dry. Since you do not want to ruin your phone or lose all the numbers in your phone book, you need to allow the phone to dry. Don’t try putting the battery back on to see if it works as this would risk damaging the phone with a short circuit. Leaving your phone in a bowl of dry rice will help to expedite moisture evaporation.

5. Heat your Phone. Apply enough heat to your phone to cause the water to evaporate without water logging your digital screen. One of the best things you can do to save a cell phone is to set it on the back of your computer monitor or TV screen over the heat vents. This is usually the perfect amount of heat to fix your phone. The convection action of the heat vents will help carry away the moisture in your phone. Leave the phone on the heat for at least 2-3 days. Another option is to leave it overnight in the oven on warm (make sure to take off the battery first).

6. Test your Phone. After you have waited 3 days, make sure everything is clean and dry looking and re-attach the battery to the phone and see if it works. If your phone does not work repeat step 4. If it still won’t work, try taking your cell phone to an authorized dealer. Sometimes they can fix it.

Tips :

* Don’t put the battery on for at least 3 days or longer if your digital screen is foggy.

* Place a piece of satin finish scotch tape over your water damage sticker before you drop your cell phone in the water to prevent the water damage sticker from voiding your warranty. This sticker can usually be found under your battery. It’s a small round white sticker, possibly with dots on it. If this sticker gets wet it changes color and your phone is marked for water damage.

* Remove the tape if you ever have to return your phone for repairs or warranty. (See the note in the ‘Warnings’ section about doing this!)

* The best way to dry out your phone is to place it in front of an air conditioner or air conditioning vent. Cold air won’t damage your phone (hot air can warp or in extreme cases even melt plastic), and air from an air conditioner is dry, and so will evaporate water faster than you might think (which is why a car air conditioner will de-mist the windshield so effectively, even if the engine hasn’t warmed up yet). Warm air from a reverse-cycle air conditioner works even better, of course. If you dry your phone in this way overnight it should be fine by the morning.

* Use a hairdryer set on warm; it won’t melt your head so your phone should be safe.* Use a food dehydrator.* Use the oven on the warm setting (make sure to take out the battery).

Warnings:

* Don’t heat the battery or it could leak acid. If you use an oven or hairdryer, make sure to remove the battery first.

* If you use alcohol make sure to do so outside, and do not apply heat in any form, not even the gentle heat of a monitor. Do not hook up the battery till the alcohol smell dissipates.

* Do not apply heat to your phone other than mentioned above. You don’t want to melt or burn your phone.

* Warranty fraud is naughty! If you dropped your phone in the can with your other ‘droppings’–are you really going to send it in for a warranty tech to have to open? Yuck!

* FYI, Most modern phones have more than one liquid damage indicator on them, only one visible to you (and sales/technician agents), and chances are, if the sticker under the battery is triggered (or would be, with the scotch tape trick), then the odds are that the internal stickers you can’t access are tripped as well. This will still result in you paying a voided-warranty fee in the long run, and it may be best to just learn from your mistake (and not make it more financially severe!).

* Even if all these steps are followed, minerals dissolved in the water can precipitate on solder and component pins, causing corrosion or shorting. Components pins are packed so closely together in a modern cell phone that even a small encrustation can create a short, rendering the phone inoperable.

Charging Faults

First of all we will discuss how many main functions a mobile phone often has irrespectively of mobile brands.

Charging faults are mainly of three types:

* No charging* Not charging* Auto charging

No charging:

in this fault a mobile phone does not charge at all when charging pin is inserted nothing happens it is always due to damaged fuse. For broken charging supply track if we repair fuse or jumper broken tracks we can set this fault off.

but on the first step I am telling you how to check no charging fault.

Check Your battery if it is not connected properly no charging fault occurs. check continuity between charging pins it should be nor full nor high resistance. If it is showing full continuity then there may be some problem in your charging IC may it is totally short you can re hot /replace this IC. If there is no continuity in charging pins 90% fuse is damaged. You can replace fuse or jumper it. if a fuse shows full continuity in multi meter then it is working correctly if it is not so it is damaged. If fuse is not damaged you can check tracks if broken. if fuse, battery and tracks are ok then charging IC would be damaged.

Not charging:

in this fault a mobile phone shows a message “Not charging” on the screen when ever it is connected with charging pins. this type of fault is not a mere hardware fault it is 90% software fault. this fault is present only in nokia and I personally experienced a problem with a nokia 3100 it was showing “Not charging” i tried hardware solutions but totally in vain so I upgraded my software now every thing was ok. . and this is the same case in many types of nokia brands you can check this up. Only nokia 1100 when “Not charging” fault comes it is very hard to remove this fault in nokia 1100 I only repaired a little number of nokia 1100 displaying this message there was a problem in charge connector diode next to charging fuse. but often it can be solved by repairing software or upgrading it.

Auto Charging:

In auto charging a phone continues showing charging despite of removing charging pin from phone. In this type of fault the “BSI” pin of mobile phone is very important because it is used to tell the phone what is the state of mobile phone charging now so if this pin is not ok this fault occurs. There are some cases in wich a mobile phone battery is ok but auto charging is present you can check transistors if used in charging section and if faulty replace it because this transistor is used in some

mobile phones to cut off charging from phone automatically. in In some cases a resistance in charging section is responsible for that which is marked as “R22″ in charging section so you can check “+” supply connection with this.

Signal Problem

No signal:

Now we are going to discuss here some important causes of no signal. if you find a handset with no signal inside it you can consider these components likely to be damaged.

* Antenna* Antenna pad* Antenna switch* antenna tracks* Rx filters* Rf Power Amlifier* or tracks* Rf signal processor (called hagar IC in nokia)

Some time you can experience that signal fault is due to damaged antenna, so you need to replace this antenna specially in SonyEricson the antenna is sticker type and it can be easily damaged so you consider first antenna in mobile phone signal faults.

Antenna pad is often rusted with corbon so you can wash it with cleaner like CTC (carbon tetra chloride) this place is often responsible for low signal faults.

!Antenna switch is the component which is most common in mobile phone signal faults you can locate this component on the top of the mother board it is in steel case often. purpose of this component is to switch between two or some time three type of frequency bands which are (GSM 900MHz , EGSM 1800MHz, PCS 1900MHz ) you may know that there are two types of waves used in our radio section one is TX (which is transmitted to others) second is R which we receive from others) antenna switch connects GSM Rx and GSM Tx with antenna pin when it found in GSM based network and in the contrary situation it contacts DCS Rx and DCS Tx pin with antenna pin so may both signal can be communicated.

Antenna tracks are the other reason to no signal so if the contacts between antenna and antenna switch are broken there would be no signal at all.

RX Filters are used to filter incoming radio waves so may no harmonics and other frequencies could get into signal processing only targeted frequency can be enter into the specific place, so some times our RX filters filter frequency we needed as well as other frequencies you can say that they block our target frequency so we can replace these filters to get it repaired. this is not in common cases but we found many faults like this in nokia 8210 no signal problem. The basic thing about radio frequency Power Amplifier is that when we need strong radio waves to spread far

around then we have to use some type of amplifier which will be able to amplify radio waves in a good power so our mobile phone uses PA(Rf power amplifier) it is used to communicate between long distances like 15-to-20 kilometers so if our PA is damaged it can not communicate and get response from the base stations.

If the supply of PA is disconnected it cannot work so signal faults can occur so you should check PA +supply carefully. The main head of the radio department in mobile phone is Rf signal processor which is often used to create, measure, calibrate and manage radio waves so if there is a problem in this signal processor you can say that there will be no signal at all, in some sets you can check they cannot be turned on without radio IC( rf signal processor) like in all nokia mobile phone you cannot power on a set without radio IC except special circumstances.

How to repair Signal problem?

Here we are discussing the techniques to repair signal faults in mobile phone first of all we are discussing about no signal condition.

Common reasons of No signal:

* antenna is not connected to phone either contacts or tracks are open* antenna switch is not switching for rf signals* some mutual coupler may be damaged* RF filters may be damaged* RF signal processor is not working* RF signal generator (VCO) is not working* software problem

Steps to be taken:

Check if antenna is properly conected to antenna pad if not then you can clean it and adjust it with pad if it is not possible then some technicians use jumper to connect antenna with antenna pad. in condition of open track between antenna switch or duplexer and antenna you can check continuity between antenna and antenna pin of antenna switch, if track is broken you can make a jumper at this place to fix this problem. Most often you may come to know that in signal problems there are lot of sets which have faulty antenna switch. so you can check it by removing antenna switch and making a jumper between RX & TX and antenna pin. It is very rare that you may come to know that the phone you are repairing has a damaged mutual coupler you can just check mutual by checking continuity between four pins in one side and of four pins in the other side but it is very rare to find a damaged mutual coupler but the chances still exist. RF filters a also very rare to find in no signal problem in mobile phones but you can’t ignore this because in NOKIA 8210 there were mostly found damaged filters in signal faults. Rf signal processor is the main component which controls the whole Rf section if the above steps fail to power on signals in mobile phones then you can consider Rf signal processor responsible for that fault, first you should know that in NOKIA & SonyEricson you can find RF signal processors in the form of BGA IC (which has terminals below its body) but in Samsung it is mostly in the form of SMT IC ( which

has its terminals at the four sides of its body) remember some time BGA ICs are suffered of dry soldering so if you find you RF signal processor in BGA form you can first check it by making reheat it and if the problem exists you can replace this IC. note ICs and IC type components has no verified checking method. so you can take a chance to replace this IC if you found problem after taking the steps mentioned above. In some mobile phones rf signal generators is used to produce a signal which is often mixed with RX received from antenna and then there is some processing on the mixed form of rf signal so if RF signal generators which are mostly known as VCO (voltage controlled oscillator) is corrupt no signal faults may occur. In the final I am going to tell you about the software function used in mobile phones your mobile phone uses its software to connect to the network and to set frequencies in mobile phones and there are some instructions found about controlling the hardware RF section by CPU with the help of software, so if the software of your mobile phone is corrupted then you may have signal faults in your mobile phone. you can see the example of all NOKIA DCT3 models if there is no “set FAID” option is checked while flashing mobile phone the phone after flashing does not show signals so don’t ignore software problems in no signal. When signal comes and then disappears. If you find a problem in some mobile phones that when mobile phone is turned on it shows signals for a while and then signal disappears after some seconds you can consider your Rf power amplifier is faulty or unsoldered or dry soldered. Explanation when we turn on the phone it shows the signal strength bars because it is receiving signals from the base station and then our phone tries to send its information about its serial number and SIM identification number to the base station and you can think that whenever phone tries to send signals to the other device it uses Rf Power amplifier (PA) and if the PA is not supporting the phone to send the informations to the base station then our phone disconnects its half way link to base station and stops displaying signals.

How to repair this problem?

First check the supply connection with your PA if supply is broken then you can make a jumper at this point check Tx signal tracks going to the PA from RF signal processor if broken then jumper it check Tx signal tracks going from PA to antenna switch if broken then jumper it. Reheat your PA. remove PA and then place two jumpers in rf in and out points at the place of PA replace PA it will be 100% right in working now.

Ringer / Buzzer Faults:

Lets see how to repair / service ringer problem!

First of all check the settings of the phone for ringer & see whether it is on or off!

Then disassemble phone & check the ringer value using multimeter on resistance mode [ see multimeter section].

The correct value of ringer should be as shown below:

monophonic ringer — 15-19 ohmsmonophonic ringer examples, nokia 3310, 3210, 2100, etc.

Polyphonic ringer—— 7-8 ohmspolyphonic ringer like nokia 6600, 6610, sonyericsson t610, etc…

This ringers always should give buzzer while checking with multimeter on a continuity mode as they all are low value resistance ..All midi, wav , mp3 , supported phones are polyphonic ringer phones & all monophonic rings supported phones are those who do not support such ringtones.

Vibrator Problem:

Same as ringer, vibrators are also low resistance. So all vibrators will also give buzzer on multimeter while checked on continuity[buzzer] mode. mostly vibrators are showing 12-18 ohms value.

Speaker Problems:

Speakers also shows low resistance value , hence checking two connectors with multimeter on a buzzer mode will give buzzer.The correct value of speaker without buzzers always are nearly 30 ohms like nokia 3100, nokia 3315, nokia 6600 etc.The speaker & ringer combined will show value around 7-8 ohms only like Samsung c100.

Mic Problems:

The Mic in mobiles are used to send voice , & if it damages the receiver will not be able to hear voice. To check mic you have to select multimeter in diode mode & it shows value at one end, & will not show value on multimeter if the multimeter leads are interchanged. Mic will never give buzzer unlike speakers & vibrators if set to buzzer mode on multimeter.