Phone Repair And Sulutions

 

The tools are divided into two groups, those needed for hardware level repairs and the tools needed for software level repairs.

For hardware level repairs

• Precision screwdriver set.
• TORK screwdriver set.
• Fine tip soldering irons.
• Hot air welder.
• Soldering paste or Flux.
• Isopropyl alcohol or Tinner.
• Digital multimeter.
• cutter.
• Soft bristle brushes.
• Pencil eraser.
• Tweezers.
• Magnifying glass.
• Adjustable power supply.

IMPORTANT!

In this course we develop everything related to repairs at the hardware level and we make an introduction to repairs at the software level, since for repairs at the software level a prerequisite is necessary, such as the correct handling of computer tools.

For Software level repairs

• PC or Notebook.
• Flashing/Unlocking Boxes (BOX), there are a wide variety for different brands/models of cell phones.
• Data cable for different equipment models. 

Security measures for our workshop and/or work table

• Count on the electrical installation with grounding on the work table.
• Wear an antistatic wrist strap.
• Antistatic blanket.
• Antistatic drawers to store spare parts.
• Antistatic accessories.

How does a cell phone work?

The first thing we need to know is how a cell phone works, and for this there is nothing better than understanding its operation through block diagrams, a cell phone is completely represented with three main blocks.

• RF module.
• AF module.
• Logic Area.

RF (Radio Frequency) Area

It is divided into two areas RX (Receive) and TX (Transmit). 

It is the area in charge of all the signal processing, both of the incoming and outgoing signal of the phone. 

The RF signal enters through the antenna to the RF receiver circuit, there is where the signal is demodulated And a filter is performed where the IF signal (intermediate frequency) comes out, which will be sent to the AF Module (audio frequency) that upon leaving the speakers they will give us Voice (audio).

But a phone is not only a receiver, it is also a transmitter, in this case, we analyze the route of the audio that enters through the microphone of the phone, the audio signal is converted into a weak electrical signal at the input of the AF Module, is amplified and sent to the RF module, specifically the RF TX circuit to be modulated and transmitted through the phone's antenna.

AF Area (Audio Frequency)

It is the area in charge of converting the IF (intermediate frequency) coming from the RF module, specifically the RX area in RF, and is in charge of converting this signal into voice, through the speaker output. In turn, it is responsible for processing the audio that enters the phone through the MIC to send it to the TX area in RF and to be transmitted. In short, this area is responsible for processing the audio of the cell phone.

Logic Area

It is the area that is in charge of processing all the input and output data of the equipment, it is similar in operation to a PC, within the logical area we will find the microprocessor, the memories: RAM, EEPROM or Flash Memory, input and output peripherals of data, display, keyboard, etc.

The microprocessor is the one who maintains total control of the phone, but based on data/instructions loaded into the phone's memory, these data/instructions form what we know as the operating system, everything the phone can do is written there.

conclusion

Why should we know what basic functions these cell phone blocks perform?

Understanding the operation through block diagrams will allow us to point out faults since, depending on the type, we will know which area of ​​the phone it corresponds to, which results in better diagnoses that will lead to the success of our repairs.

IMPORTANT!

In later chapters we will be indicating how to identify these areas on different cell phone plates.

An example: 

If we have problems making calls with a cell phone, and it indicates System Busy on the screen or it gives us fast busy or calls drop, we would have to verify the RF area of ​​the phone, specifically TX in RF, since RF is It is responsible for signal processing and specifically TX is responsible for the outgoing signal of the phone, the details will be expanded in later chapters.

Blocks of a cell phone – Typical faults

The following graph shows the main blocks of a cell phone and the common faults that we can find in each block, in later chapters we are indicating how to locate these blocks on the plates of different cell phone brands/models.

Conditions for a cell phone to work properly

1. The operating frequency of the operator must be compatible with the operating frequency of the cell phone 

2. The cell phone must not have SIM Lock with the SIM Card to be used 

3. The electronic serial number of the phone (IMEI), must not be in negative band 

4. Configure multimedia services

The operator's operating frequency must be compatible with the frequency supported by the cell phone

For example, in GSM there are the following operating frequencies: 850, 900, 1800 and 1900 Mhz, that is, if the operating frequency of an operator is 850 Mhz and we want to use a phone that does not support this frequency, for For example, a European serial telephone that only works in the range of 900, 1800, 1900 Mhz, the cell phone will not work, that is, it will not be able to pick up a signal because it is not in tune with the operator's frequency.

Example. 

“It is like wanting to listen to a radio station that transmits at 100.9 Mhz with a radio tuned to another frequency, that is, we could not listen to the station because we were not in tune.”

The cell phone must NOT have SIM Lock with the SIM Card to be used

It means that the cell phone should not be blocked for the SIM Card to be used, since certain operators block their phones in such a way that they only work with their SIM Card.

The phone's Electronic Serial Number (IMEI) must not be in the negative band

In other words, the serial number of the equipment (IMEI) must not be reported since the terminals, when registering, send the information of the phone's IMEI to the Operator and if it is found in the database of series reported in the EIR, they send commands restriction to the line and will not be able to use the equipment.

Configure Multimedia Services

1. Internet access 

2. Sending MMS (Multimedia Messages)

IMPORTANT!

If we have problems with a cell phone, they must first verify the conditions for proper operation, and if they meet all the indicated conditions, we would be facing a cell phone with a fault.