The most complete mobile phone fault repair method inventory: you can also repair
The mobile phone is a must-have electronic product for everyone. It has convenient communication and access, and has all kinds of functions such as Internet access. Through the mobile phone function, you can contact friends who are separated from yourself by any means, no matter where you are, and you can also check the online information anytime, anywhere. You can also share your own personal information with friends and other users, but these functions will be wiped out if the mobile phone fails, but the mobile phone can be restored to normal state through mobile phone repair and maintenance, and Xiaobian carefully organizes some common mobile phone faults. Judging maintenance skills for beginners and mobile phone enthusiasts:
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First, the inquiry method
When you get a faulty mobile phone, first ask the user, under what circumstances, if there is a fault, whether it has been repaired, etc., in response to the user's reaction and the phenomenon of the fault, determine the location of the fault, such as being dropped. Mobile phones, should consider mobile phone chip solder joints, breakpoints, component dropout, circuit board breaks, etc.; water inlet, consider power module damage, copper foil and pin rust, corrosion, disconnection; Whether it has been moved or exchanged, whether the components are installed or not.
Second, intuitive
After the inquiry and then visual inspection, some faults can be found. If there is a crack in the outer casing of the machine, focus on the components on the circuit board that are corresponding to the falling, whether there is any falling off or disconnected; there are water stains on the main board of the water inlet, even the artificial embroidery, there are debris between the pins, etc.; Not normal, see if there is any oxidation caused by oxidation at the button point; use the blowing method to judge whether the microphone and the microphone are normal.
Third, the resistance method
Usually pay attention to collect the resistance value of some parts of some mobile phones. Such as power reed, power supply filter capacitor, SIM card holder, chip pad, integrated circuit pins and other ground resistance values. When the mobile phone is being repaired, the fault can be judged according to the magnitude of the resistance value of the ground to a certain point. If the normal resistance of a certain point to the ground is ten thousand ohms, the resistance of the faulty machine at this point is much larger than ten thousand ohms or infinity, indicating that this point has been disconnected. If the resistance is zero, the point has been short-circuited to the ground; the resistance method is also used for Determine whether there is any disconnection between the lines and the quality of the components.
Fourth, the voltage method
For a normal mobile phone, the corresponding point voltage is a fixed value. Once the mobile phone is damaged, the voltage value at the fault will inevitably change. By detecting whether the voltage value is normal, the fault occurrence location is quickly found. If the voltage is zero, the power supply is indicated. The circuit has an open circuit; the voltage at a certain place is lower than the normal value, as long as the power supply is normal, indicating that the load has a problem; when measuring the voltage, it is also necessary to pay attention to whether the continuous DC power supply or the pulsating DC power supply.
Five, current method
The value displayed on the current meter on the maintenance power supply is the sum of the currents of the units in the mobile phone. The current under different working conditions is basically regular. If the mobile phone fails, the current will change constantly. The experienced maintenance personnel pass different The current value can roughly determine the fault location. For example, if the power is applied, there is a current of several tens of milliamperes, indicating that the component connected to the positive pole of the power supply is leaking; if the current is greater than 500 mA, the CPU or power supply, power amplifier, and power supply filter are indicated. Components such as capacitors have a breakdown short circuit.
Sixth, comparative method
There are comparisons to identify. When the mobile phone is being repaired, when the model, position, voltage value, current value and waveform of some components are considered abnormal, the corresponding parts of the same type of normal machine board can be used for comparison. For example, if the position of the double triode, whether a resistor or capacitor is incorrectly installed, whether the resistance is normal, whether a certain two points are connected, etc., the fault can be detected quickly.
Seven, the replacement method
When you suspect that a component has a problem, you can remove the same component installation experiment from the normal phone, the effect is immediate. If the fault is removed after replacement, the original component is damaged. If the fault still exists after the replacement, the problem is not in this component, and the search should continue. The alternative method is applicable to all components in the mobile phone. In some cases, single-frequency components can be used instead of dual-frequency components. For example, the 14-series single-frequency amplifiers are used instead of Hitachi's dual-band amplifiers, but they can only be used in areas with only the GSM band.
Eight, the temperature sense method
Commonly used for large currents caused by small current leakage or component breakdown. If the mobile phone is powered on, there will be tens of milliamperes of leakage. Although it does not affect the use, the standby time of the battery is greatly shortened. During the overhaul, the supply voltage can be increased, and the leakage current can be increased. The hand or face and the lip body are hot sensitive parts. Look for the heating element, which component is hot or damaged; you can also use a loose cigarette smoked circuit board to apply a layer of white mist on the component. After power-on, observe which component the fog layer disappears first, that is, the heating element; That is, there is a large current of 500 mA or more, and the power supply voltage can be adjusted to make the current not exceed 200 mA (do not expand the fault). After power-on, use the above method to find the starting thermal component and replace it.
Nine, pressing method
Used for various faults caused by poor component contact or solder joints. If the phone is not turned on when booting, suspected font or CPU soldering, you can press the thumb and index finger on both sides of the chip to press it properly. If you press a chip, you can turn it on, that is, it can be soldered.
Ten, short circuit method
It is often used for emergency repairs when some components are damaged. For example, when the antenna switch, the filter before and after the high-amplifier, the combiner, the power amplifier, etc. are damaged, the hand is not present at the moment, and the input terminal and the output terminal can be directly short-circuited (the antenna switch is short-circuited). After the mobile phone can only work in one frequency band), if the mobile phone returns to normal after the short circuit, the component is damaged.
XI. Open circuit method
It is to disconnect the suspect circuit or component. If the fault disappears after disconnection, the problem is on the disconnected circuit. For example, when the power is applied, the power amplifier is directly powered by the power supply. The inductance or resistance of the power supply branch can be removed, and no large current is generated, indicating that the power amplifier has been broken and damaged. If there is no signal after installing the SIM card, there is no signal after the card is installed. Signal, suspect that there is a problem with the amplifier, you can also disconnect the power supply or amplifier input channel, if there is a signal that the amplifier is damaged.
Twelve, hanging method
It is mainly used to repair the power supply circuit of the mobile phone with or without breaking, simple and practical, convenient and fast. The method is: the positive end of the maintenance power supply is connected to the ground end of the mobile phone (negative pole), the negative pole of the maintenance power supply and the positive electric terminal of the mobile phone are not suspended, and the positive pole of the power supply is added to all circuits in the circuit that can pass the direct current. The oscilloscope (or multimeter, the ground is connected to the ground of the maintenance power supply) to measure the part of the circuit that you suspect is broken. If there is voltage, there is no open circuit; if the voltage is not detected, it is an open circuit (or empty point).
Thirteen, cleaning method
When the mobile phone enters the water or enters the dust for a long time, the insulation resistance between the components is reduced to cause some malfunction. It can be solved by a new cleaning with an ultrasonic cleaner. For example, most Samsung mobile phones have a "system failure, please contact the system service provider". Most of them are caused by the clock connected to the external device and the leakage or short circuit of the components on the data transmission line. The tail plug can be cleaned first. You can do it; if you can't rule out, you can remove these components. If the button caused by oxidation fails, it can be scrubbed with water or alcohol.
Fourteen, waveform method
When the mobile phone is working normally, the signal waveforms of the circuit under different working conditions are also different. When troubleshooting, use the oscilloscope to measure whether the signal waveform is normal, and quickly determine the location of the fault. If there is no signal during the maintenance, first check whether there is a normal receiving baseband signal to determine whether it is a radio frequency circuit or a logic circuit. If there is a normal receiving baseband signal, the radio frequency circuit is normal, the problem is in the logic circuit; when the maintenance is not transmitted It is also possible to measure whether there is a normal transmit baseband signal to determine whether the fault is caused by a logic circuit or a radio frequency circuit.
Fifteen, signal method
It is often used to repair mobile phone RF circuits, input a fixed frequency with a signal generator, detect whether there is normal waveform data on the signal path, and determine the fault location. If a wire is used on the power line for a few turns, the sensing signal is used to touch the antenna of the mobile phone, and the presence or absence of clutter on the receiving channel is detected to determine the fault. For Motorola mobile phones, you can also use the test card or the tester to load the test function to detect whether the function of receiving, transmitting, etc. of the mobile phone is normal, or you can enter the transmitting state to perform maintenance on the transmitting circuit.
Sixteen, software law
The power supply voltage is unstable, the temperature is improper when the memory is blown, or the software program itself is faulty, and the performance of the memory itself is not easy to cause the software data to be lost or disordered, resulting in no power on, no network or other software failure, usually rewriting the software with the disassemble maintenance instrument. The data is solved. If it is not online, the font or chip can be removed and programmed with 48 programmer. If the write fails or the font is damaged, the memory itself is damaged.
Seventeen, repair welding method
During the use of the mobile phone, the keys are frequently pressed, flipped, and dropped. It is prone to various faults caused by virtual welding or poor contact. The faulty part is observed through a magnifying glass or pressed to solve the problem.
Eighteen, flying line method
When the mobile phone is dropped or the chip with the encapsulation is removed, the drop of the pad is a common occurrence. In addition to the empty point, the useful drop point is solved by the flying wire, usually on the lead or component connected at the point. After connecting with the fine enamel wire, use the tweezers to bend the insulated lead head into a circle of solder joint size at the drop point of the pad, fix the lead with green oil, and bake under the purple light (usually the violet light detector). Minutes or so. The disconnection outside the chip can also be solved by the flying line method.
19. Antenna method
Simple and practical, when troubleshooting RF circuits, use a long wire of about 10 cm or a tin wire, tweezers, oscilloscope probe as a dummy antenna, respectively connected to the input and output of the signal path, such as a dummy input at the input of a component. The antenna phone works normally, indicating that the circuit behind the dummy antenna is normal, and then the dummy antenna is moved to the output end of the component. If it does not work properly, the problem lies in this component.
Twenty, adjustment method
When the transmission signal is too strong, such as the transmission shutdown, the transmission reset, the redial caused by the weak, etc., if the power amplifier or the power control circuit is inspected or replaced, the component values ​​in the relevant circuit can be appropriately adjusted to achieve the repairing purpose. Such as Motorola V998 and Nokia mobile phones, due to excessive transmission power caused by the transmission shutdown, can increase the resistance in the power control circuit to solve; if the transmission red power caused by the transmission redial can reduce the preamplifier base supply resistance, increase The amount of preamplifier is amplified so that the phone works normally.
Twenty-one, distinction
When the maintenance signal is abnormal due to the control signal or the power supply circuit, the same DC voltage in the circuit can be led according to the value of the control signal or the power supply voltage to distinguish the fault area. If the circuit can work after power-on, the controlled circuit is normal. The problem is in the control or power supply circuit. If the circuit is still not normal after power-on, the problem is in the controlled circuit. For example, the control signals of the RX-EN, TXEN, DM-EN, -5V-EN and T2688 RF power supply tubes of the Motorola V998 are all 2.8V signals; if not normal, the 2.8V output of the power supply can be added to the corresponding signal. On the control end (to disconnect the original control line), if the circuit is normal, the control circuit is normal, and the control circuit for generating the control signal is important; otherwise, the fault is in the controlled circuit.
Twenty-two, analysis
Only by understanding the structure and working principle of the mobile phone can we analyze and judge according to the phenomenon of the fault, and quickly find the fault location. If you don't understand the working principle of mobile phones, relying on memory and experience to repair mobile phones, you will not analyze and judge the faults. You can't jump out of the circle of "one blow, two washes, and three movers", and you will definitely take a lot of detours.
Twenty-three, comprehensive law
Everything is familiar, and repairing the phone is no exception. The fault of the mobile phone is nothing more than the hardware and software. As long as you understand the structure and working principle of the mobile phone, it will analyze and judge, comprehensively apply a variety of maintenance techniques, and cooperate with the corresponding maintenance equipment, as long as the fault of repairing the mobile phone is not A very difficult thing.
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