1. Single key failure: Because the key adopts coordinate type, the single key failure is mainly due to the surface pollution of the single key or the falling of conductive powder, which makes the high and low contacts of the key unable to conduct, resulting in no instruction being sent to the CPU. Clean the key or replace the conductive film of the key.
Example: Nokia 82 10, after repairing the RF fault, the installation machine found that the 3,7 keys were out of order. After disassembling the machine, the rosin on the 3,7 keys was cleaned with cotton swab alcohol, and the installation machine was fine.
2. All buttons are out of order: CPU can't accept instructions from two buttons at the same time, so as long as one button is on, the other buttons will no longer work. Treatment method: ① clean the key; ② Check and adjust keys that are easy to press, such as side keys. In addition, for Amoi A8 and other mobile phones, a rheostat is connected in parallel with the high-level terminals of the keys. If a rheostat ages, all the keys will be invalid.
Example: A T66 mobile phone received by Lixin failed to connect all the buttons, and even failed to turn it off. After disassembly and inspection, it was found that the conductive film powder of the "C" bond fell on the bond, which made the "C" bond "crushed to death", and it was OK after cleaning with alcohol cotton.
Tip: This kind of fault is mostly caused by the model using conductive film. If the housing has been replaced, please pay more attention to the side key jacking. It is also necessary to correctly distinguish between the crash fault and the key failure fault. Generally speaking, a phone call can be made for a key failure (connected but not answered), and a phone call cannot be made for a crash failure.
3. Row or column key failure: the failed row or column cannot communicate with the CPU normally.
① Check the faulty line or column connection to CPU.
(2) welding CPU (there can be no glue under CPU).
Tip: Many mobile phones that connect the front panel with a straight bracket or cable are prone to this kind of fault.
The second measure: double thunder is used to ears-specializing in receiver failure
Judgment: Pull "1 12" to measure whether there is a jump voltage at the receiver contact. ① There is tripping voltage: the fault lies in the receiver or poor contact. Clean and adjust the receiver contacts and replace the receiver. ② There is a jump voltage at one end and no jump voltage at the other end: most of them are disconnected between the receiver and the audio IC. 3. There is no voltage jump at both ends: most of them are virtual welding or audio IC damage. 4. The noise in the receiver is mostly caused by the deterioration of the small filter capacitor on the receiving line, which can be improved by indirectly connecting a capacitor at both ends of the receiver. In addition, receiver damage and microphone failure can also cause receiver noise, and audio IC failure can also cause receiver noise.
Tip: Many mobile phones integrate audio into the power IC. If there is a jump voltage at one end and no jump voltage at the other end, the end without jump voltage can be grounded.
The third measure: the tiger's mouth pulls out the tooth-specializing in failure to deliver a baby;
Dial "1 12" to measure whether a contact of the microphone has a voltage of about 2V. ① There is voltage: the fault mostly lies in the microphone or poor contact. Clean and adjust the contact, and replace the microphone. ② No voltage: Most faults are that the audio IC is disconnected from the microphone or the audio IC is damaged. You can try to pull a voltage of 2V to the positive pole of the microphone first, or you can solve some problems. 3. Some mobile phones have special earphone switch control tubes, which are easy to be soldered or damaged. 4. Noise faults are mostly caused by the deterioration of the filter capacitor, and the deteriorated capacitor can be replaced. It can also be improved by adding a capacitor between the two poles of the microphone.
Tip: There are often articles about how to change hands-free to solve the problem of answering and calling, which is a very practical technology.
The fourth measure, the key-specializing in the display failure:
There are many manifestations of display failure: 1, and the display line is insufficient-it is usually caused by the damage of the display screen and must be replaced. 2. When it is not displayed, the screen is reversed, and the screen is displayed-for cables, it is generally necessary to check and replace the cables first; For those without cables, it is generally caused by aging of conductive adhesive or virtual welding of display interface. 3. Display a black screen or a bright screen-it is mostly caused by the deterioration of resistance and capacitance on the display circuit, which can be improved by replacing the deteriorated capacitance and changing the resistance value of the contrast adjustment resistor. 4. No display-whether the fault is on the motherboard can be judged by replacement method, and the fault point can also be basically judged by analyzing the cause of the fault. If there is information, it can be judged by measuring whether the display voltage is normal.
Tip: except for individual working voltages, the display circuit is directly related to the CPU. Generally speaking, the appearance of the display screen is intact and the possibility of damage to the display screen is very small.
The fifth measure: the brilliance of the sun and the moon-specializing in the failure of no background light
There are two kinds of background lights: light-emitting diodes and luminous paper. At present, the background light of color screen mobile phone is also composed of light emitting diodes (white light, usually composed of three lights, many of which are connected in series, and the power supply voltage is provided by the booster circuit). For the LED, repair it according to the following steps:
(1) If individual lights don't work, they are mostly broken and can be replaced.
② Test whether the power supply of the backlight is normal, which is usually connected to the battery voltage, if there is no flying wire. Measure the connection between the control tube and the background light.
③ Weld or replace the background light and keyboard light control tube.
Luminous paper generally needs an AC voltage of about 150V to work normally, so it has a matching boost conversion circuit, which consists of a boost coil, a boost conversion IC and an energy storage capacitor. The maintenance process is as follows:
Use a multimeter to measure whether there is an AC voltage of about 150V across the LED. If yes, the LED is damaged and can be replaced. If not, check whether there is an AC voltage output of 150V, an input of about 3V, whether the booster inductor is damaged, and whether there is a control signal. Find the fault points in turn.
Tip: Glowing paper is fragile. The cable damage of flip phone can easily lead to the failure of no background light, which can be solved by flying wire or replacement. There is no reflective paper installed behind the display screen of color screen mobile phone, which will cause dim background light. (Reflective paper and light guide plate are installed in the color screen, which affects the backlight brightness. )
The sixth measure: out of nothing-specializing in the failure of reading cards.
The SIM card or UIM card holder has six feet. First, use the buzzer of multimeter to check the grounding of SIM card or UIM card holder. The power pin is opposite to the grounding, and then rotate clockwise, followed by reset pin, clock pin, data pin and online programming pin.
① Under normal circumstances, the power supply pin has a 3V power supply. In the case of disconnection, you can find a 3V voltage flying wire to force power supply.
② If you measure the reset, clock and data line with a multimeter, you can see the unstable voltage less than 1V (if possible, you can measure it with an oscilloscope). If you don't have a foot, you need to find the corresponding line.
For GSM mobile phones, the above measurement must be made at the moment when the mobile phone is turned on, because if the CPU cannot read the card information, it will terminate the contact with the SIM card. For CDMA mobile phones, except the data pin, it can be measured as long as it is turned on.
The seventh measure: the golden snake dances wildly-specializing in the failure of silence.
Please note that the phone will not ring in "conference mode" or "silent mode".
① Measure the ringing quality, and replace it if it is not good.
(2) Test whether the ringing power supply pin has power supply. If there is no power supply, you can find a 3V flying wire.
3. Weld or replace the ringing signal amplifier tube.
4. Judge whether the IC outputting the ringing signal is damaged.
5. Chord ringtones are generally completed by special music ic (Yamaha chip). (Generally, 17# and 18# are output pins)
Tip: Ringing failures are mostly caused by the falling of the mobile phone, which leads to the disconnection of the ringing foot or the attenuation of the ringing function. I recently made a topic in the technical theory area about the position of chord ic and its maintenance methods. Welcome everyone to have a look.
The eighth measure: the backyard caught fire-the special treatment machine failed to charge.
① The mobile phone plugged into the charger has no charging response-generally speaking, the mobile phone has not detected the fault of the external battery. Common ones are damaged charger, battery in low-power sleep state, and damaged mobile phone tail plug.
(2) Insert the charger into the mobile phone to show that the charging is completed quickly-generally, the battery is damaged or the charging detection circuit is faulty.
(3) Charging when the charger is not plugged in-there is a voltage connected in series on the tail plug charging circuit, or a short circuit on the charging control circuit, resulting in an error signal from the CPU. The common reasons are short circuit of tail insertion and leakage of protective capacitor on charging circuit.
After any mobile phone has a charging failure, the battery voltage of the mobile phone should be measured first. If it is 0V, it means that most of the batteries are asleep (some brands are asleep when the batteries are below 3V). You can use a regulated power supply to force charging, and then test the charging situation of the mobile phone. If the battery is forcibly charged with a regulated power supply, it is found that the ammeter does not move, which generally indicates that the battery is aging, and there are faults such as full charging and low use.
Tip: The design of different models of charging circuits is quite different. Some mobile phones have special charging IC, some have power IC for charging control, and some have several components to form a charging control circuit. But the failure rate is relatively low.
Additional: special handling of mobile phone standby low battery alarm;
There are many factors that cause the low battery alarm of mobile phones; Battery contacts, power IC, CPU, audio, software, etc. Relatively speaking, there are two main treatment methods:
1. The battery power detection circuit is abnormal, causing a low battery alarm. Generally, the battery voltage is divided by two resistors to obtain a voltage of about 1.8V, which is sent to the CPU or audio for detection, and then the CPU sends out power information to the display screen and makes an alarm or protective shutdown action. This kind of aircraft needs to detect the divided voltage to determine whether it is a line fault or a CPU fault. Samsung mobile phones mostly use this circuit.
2. Low voltage alarm caused by audio IC. The battery charge detection of many mobile phones is done through audio IC. The judgment method is that if the low battery alarm stops after the audio IC is removed, it must be that the audio IC is damaged. Siemens, Ericsson and other mobile phones all use this circuit.
3. Low power alarm caused by software. In the process of power detection, the software must provide detection parameters, so that the deviation of parameters or the set threshold is too high will cause the low battery alarm of the mobile phone.
The ninth trick: soaring to the sky-specializing in the treatment of large current leakage faults
The large current leakage is mainly caused by the damage and short circuit of power IC, power amplifier and power control tube directly supplied by battery voltage. Some will also have short-circuit protection connected to a regulated power supply.
(1) Use the buzzer of the multimeter to measure whether the two ends of the capacitor around the large part are grounded. Generally speaking, the large component next to the capacitor whose two ends are grounded, that is, the faulty component, can be replaced.
(2) After the regulated power supply is connected, touch the element by hand, and the heating element, that is, the faulty element, can be replaced. For short-circuit protection of mobile phones, we can reduce the voltage, maintain a leakage current, and then touch.
Tip: Soaking machines and humidifiers are prone to leakage faults, while the large current leakage of normal mobile phones is mostly caused by power amplifier and power supply faults.
Ladies and gentlemen, there is a saying that seeing is believing and seeing is believing. A master makes a mistake, and the victory or defeat is within a millimeter. When he sees the confession, he will change, and so will the enemy. He is as flexible as a monkey. When the enemy's flaw is discovered, it will be a winning blow with great power.
The tenth trick: fight poison with poison-specialize in treating small current leakage faults.
① Raise the voltage to 7-8V, and then touch the machine board with your hands. If the component is found to be hot, it is considered that the component is partially damaged and can be replaced.
(2) Carefully check whether there is corrosion and short circuit on the resistor and capacitor on the line connecting the battery voltage, and the damage of the capacitor resistor will also cause small current leakage.
3. Several battery voltage lines can be listed separately, and then cut off separately, so as to judge the fault point.
Tip: Small leakage current is relatively difficult to check, which requires careful and patient observation and analysis. In actual maintenance, small leakage current is not easy to be found by voltage regulation touch, so it is very important to understand the circuit. Many small leakage currents will lead to the failure of the self-test of the mobile phone and it will not be turned on.
Eleventh trick: chop and change-specializing in time failure
1, time does not go, time is not allowed, time cannot be set-generally 32. The real-time clock crystal oscillator of 768 is damaged and can be replaced.
2. The time to restore to the original factory settings after replacing the mobile phone battery, or the time to restore to the original factory settings immediately after restarting-all are caused by the failure of the spare battery or the charging circuit of the spare battery.
3. Time sometimes jumps irregularly-all software failures.
Tip: Generally, the 32.768 real-time clock crystal oscillator is used, and so is the spare battery. If the time is zero after the battery is recharged, the voltage of the spare battery should be measured first, and then the regulated power supply should be connected before judging whether the spare battery is charged. So as to quickly judge that the charging circuit of the spare battery is out of order. If there is something wrong with the charging circuit, generally pull a stable 3V voltage flying wire to the positive pole of the nearby spare battery.
Twelfth trick: hit it off-specialize in automatic shutdown failure
Automatic shutdown is generally divided into two situations, one is automatic shutdown in use and the other is static automatic shutdown. Generally speaking, the former mainly investigates poor battery contact and virtual soldering of mobile phone motherboard components, while the latter is mainly caused by the failure of mobile phone logic circuit. Generally, we can seek solutions from power supply, clock circuit, software and so on.
Thirteenth measure: hair-trigger-specially start the shutdown and start the low-voltage alarm.
This is mainly caused by the high current operation of the transmitting final circuit. The main components involved are power amplifier, power amplifier power tube (except some directly supplied by battery voltage), power control and other components in the final transmission circuit. Of course, bad batteries sometimes cause this kind of failure, which can be distinguished by connecting a regulated power supply and observing the emission current. When the mobile phone is in the transmitting state, the power amplifier works and sends out two signals, one of which is transmitted from the antenna through the antenna switch, and the other is sent to the power control as a sampling signal, and then the power control sends out the power amplifier level to control the amplification level of the power amplifier. When transmitting, if the current is too large, the voltage of the whole machine will be pulled down, and the mobile phone will give a low battery alarm, and it will be turned off in severe cases.
Tip: The power amplifier is a wearing part, and most of the power amplifier failures are caused by its damage. The power amplifier is expensive, especially the black power amplifier is extremely resistant to blowing. Pay attention to the temperature when blowing welding. At present, there are more and more styles of power amplifiers, but they are generally inseparable from the four basic points of output, input, power supply, control and grounding. Most black power amplifiers are detachable and short-circuited, and can be used normally in strong signal areas.
The seventeenth trick: both soft and hard-specialize in software failures.
The main manifestations of software failures are: crash, low current power failure, crash after card insertion, crash during phone call, bump (0)| smash (0)| reply | report what you have commented on! 3rd floor-:March {2009. 18 20: 37: 16 modified, crashed after entering the menu, etc. Generally speaking, faults caused by internal programs can be called software faults.
The essence of software failure is often divided into two situations: one is the real software failure caused by program disorder or data loss, and the other is the program failure or incomplete operation caused by physical damage of fonts, which is essentially a hardware failure.
General processing flow of software fault:
1, welding or replanting fonts. It is mainly caused by virtual welding, which is generally manifested as uncertain fault phenomena such as not starting for a while and crashing for a while.
2. rewrite the software. Writing software can be divided into two types: disassembly-free and disassembly-writing.
The advantage of disassembly-free machine is that it can reduce the risk of physical damage caused by disassembly. You can see the actual problem through the online situation of the instrument. Generally speaking, if you are online normally but can't finish writing completely, it means that the font is partially damaged. If you can't go online, the font is damaged or the communication with CPU is not normal.
The advantages of disassembling and writing are: the data source is extensive, not limited by data lines, and there is no need to update the instrument for a certain period of time.
3. After rewriting the software, if there are abnormal phenomena such as crash, no boot, no screen display, and out-of-order keys, it is generally that the written software version is wrong and correct data needs to be rewritten. How to judge whether it is correct information? One depends on accumulation and the other on observation. Generally speaking, the size of written data should be close to the size of read data. For example, if the data you read is 8M, but the data you write is only 6M, you can conclude that it is not valid data.
Special reminder: mobile phones can't read short messages, can't enter the phone book, can't store the phone book, and have no call records. Generally, the register is partially damaged, not a font or software problem. The temporary memory must be replaced before the problem is solved.
[Post Bar] The 18th trick: Save the dragon and the tiger-specialize in the fault that can't open the small current.
It is very common that mobile phones are not turned on with small current, and maintenance is also difficult, mainly involving more detailed tests. If it is a three-no mobile phone with no map, no data and no reference, it can only be explored by experience.
To turn on the phone, you need a power supply first. There are two main power supply modes for various types of mobile phones, one is complete power supply for the whole machine, the other is step-by-step power supply, and the latter is controlled by programs.
With power supply, CPU can work. Generally speaking, the CPU needs two power supplies, one is VBB, which is generally about 3V, and the other is VCORE, which is generally about 2 V.
Of course, the CPU also needs a clock signal to provide its working rhythm, and it can't be done without this CPU.
The CPU also needs a reset voltage, generally 2.75V V. Without this voltage, it will be unable to continue working because of overflow. In addition, individual models must also provide battery information needed for CPU operation.
After the CPU is started, it starts to call the programs in the font, and at the same time, the register works, providing a space for temporarily storing data. Whether the communication between CPU, font and temporary storage is smooth or not also directly affects the startup.
Generally speaking, for GSM mobile phones, the power consumption of the main clock circuit is about 10MA, the power consumption of the CPU is about 20MA, and the power consumption of the font and temporary storage is about 20MA. Therefore, if we carefully observe the current response at startup, we can see two obvious current boosting phenomena. Only in this way can it be a normal startup response. If the current is directly above 50MA, it is generally necessary to think about the inspection from the perspective of whether the power supply and power consumption are normal.
Low current 10MA does not start-first check the power supply and 13M clock circuit.
Let go of low current 20MA-CPU is not started. Check the working condition of CPU and whether it is damaged.
The current is 30MA, and in most cases, it will not fall back immediately after it is released-the focus is on font, software and temporary storage.
In addition, the fault point can be identified by repairing the connection between the instrument and the mobile phone.
The feasible maintenance methods for this kind of fault are: experience first, first soft and then hard, measurement-oriented, and finally.
In actual maintenance, the faults of mobile phones are ever-changing. Consulting more experts, reading more relevant materials and learning more are the best ways to make progress. Only in this way can the skills be deepened and you can be comfortable. It looks easy, but it is difficult to learn. Let's practice. It belongs to paste and copy (I hope I can help you)