MOBILE FAULT TRACING SECTION

Dead Set Repairing We are going to discuss here some techniques and steps to repair dead condition in mobile phones irrespectively of brands  First of all let us now about the main functions to power on a mobile phone you can consult our previous lesson

1. Key Componentsand funtions: 
· Battery 
· Power Switch 
· battery terminal 
· Power IC 
· Oscilator 
· 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 funtions 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 wether they are connected with the power IC of not if not then you can make a jumpwer 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 alwways 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 funtion" so if a power on funtion is faulty the whole unit will not power on. but there are some problems with ICs that we cannot check them wether they are working right or not rather we can only assume that they are faulty if the other functions are correct. 

Oscilator:
An oscilator 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 funtion which is used in mobile phones to divide clocke frequency to get accurate frequency to run digital components so if divider is failed power on fault mat occur. This frequency dividing funtion 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 funtionality is very necessory in mobile phones while testing in boot process but its functionality is assosiated 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 to Repair Dead Set

Note
Some steps which cannot be take in an average mobile phone lab are avoided to be explained becaues oscilator and divider's functionality can be cehecked by Osciloscope which is not available in an common mobile phone lab.

sp� 1 s a �Oi �w pple-style-span>

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 mobilephones 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

� - p �w �zx /span> for complex multi-stage filtering operations, digital filters have the potential to attain much better signal to noise ratios (more of desired signal in comparision to unwanted signals) than analog filters. This is because whereas at each intermediate stage the analog filter adds more noise to the signal, the digital filter performs noiseless math operations at each intermediate step in the transform.

The primary source of noise in a digital filter is found in the initial analog to digital conversion step, where in addition to any circuit noise introduced, the signal is subject to an unavoidable selectivity error due to the finite resolution of the digital representation of the signal.

Digital filters can achieve virtually any filtering effect that can be expressed as a mathematical algorithm. The two primary limitations of digital filters are their speed (the filter can't operate any faster than the computer at the heart of the filter), and their cost. However as the cost of integrated circuits have continued to drop over time, digital filters have become increasingly commonplace and are now an essential element of many everyday objects such as radios, cellphones, and stereo receivers. Digital filters can easily achieve performance levels far more than what is (even theoretically) possible with analog filters. It is not particularly difficult, for example, to create a 1KHz low-pass filter which can achieve near-perfect transmission of a 0.999KHz input while entirely blocking a 1.001KHz signal. Analog filters cannot split apart such closely spaced signals.

Mobile Phones make use of Filters called Dual Band-pass filters because they need to allow two frequencies of signals most commonly 900MHz and 1800MHz in the dual band mobile phones. Also Antenna Switches are used in Mobile Phones expensively at the very first stage of the point of entry of the signal (called the received signal Rx) into the mobile phone which also eventually becomes the point of exit for the outgoing signal or the transmitted signal Tx. The newer models of the Mobile Phones like a Nokia 6600 makes use of an active Antenna Switch which also has a built-in amplifier circuit inside it to immediately boost the Rx signal.