subject: Maintenance knowledge of cell phones [print this page] Maintenance knowledge of cell phones Maintenance knowledge of cell phones
1 When press the opening key, nothing happened with the ammeter. This situation is often happen under the state that power circuit is abnormal, and the main reasons are as follows: (1) power can not be sent to the power supply integrated circuit because the break of the contact pad, in general, the positive pole of the battery is in common with a large capacitor in motherboard and IC's power supply side. This can serve as an important basis for our determining whether the battery's power have been sent normally. (2) If there are some problems with the opening button, we can clean this button with an eraser, and then the problem of poor contacting can be removed. (3) The contacts between the opening key and the power IC are not really welded together, and this problem is commonly known as the fault of cell phones opening keys. For beginners, they have no idea with this problem, they can check it if they have circuit diagram, but if not, and they don't know how to start. In fact, at this time we can do something: firstly, we should look at if we can open the cell phone with plugging in a charger; secondly, make a routine examination of the cell phone's power line. And when we make a routine examination of the cell phone's power line, on one side, we can replace the front panel to see if the front panel's circuit is closed, on the other hand, we should emphases on the examination about the boards before and after, to see whether they are in the poor state, or if there are factitious welding, and thirdly is welding power supply IC again.
2. When we press the opening key, the current can not reach its maximum. This fault comes from the RF circuit or sending path. Because the emission current of amplifier is higher, we can determine whether the current have been launched by observing it. Under normal circumstances, when the cell phone start search network after opening, the ammeter should have a jump, but because different kinds of cell phones have different current, so we can not say what value the current should reach is normal, and generally the current can achieve more than 300mA, and this mainly refers to that the cell phones can be switched, but is not open normally, or there are no problems with receiving and transmitting when it is open.
3. When press the opening key, the ammeter have some reaction, but not swing, and the current can only be maintained at a few MA, the maximum will not exceed 50mA. For this situation, we can sure that the CPU doesn't start to work normally. And the CPU can not start to work, and this Often because that character and temporary data can not be read by CPU. This is mainly a software problem. And for this problem, we should deal with the software. Of course, there are a considerable number of cell phones whose false hardware and software failures have caused many problems, and this often be seen in the series of cellular phones made in China such as Samsung, Bird, TCL and Capitel, etc. And there we need to focus on reminding the general maintenance staff that the keyboard matrix circuit of cell phones is also a key and also can lead to this problem. The reasons are as follows:
The problems of the software.
The end plugs' leakage.
The capacitor and voltage regulator tube which are connect with the Font Chip leak power.
Back-up batteries' leakage
CPU font's factitious welding.
The damage of 32.768kHz.
The cables short-circuits of some cell phones' keypad can also lead this problems.
4. When press the opening key, the ammeter pointer reach to full grid immediately. This is mainly because there is a short circuit within the cell phone or the leakage of filter capacitor. The normal circumstances should be the current is about 200mA instantaneously after opening, and when the cell phone is in standby state the current is around about 50 ~ 100mA and the pointer keep swinging. In addition, current is about 300mA when it is being launched, so there is a jump from standby to launch. If power-high current occurs when we charge the cell phone, then we need to focus on the examination of B + circuit which related to cell phone circuit, such as Large filter capacitor, power supply IC, switch control tube, power supply control logic, RF power management, power amplifier, vibration device, etc. In fact, in routine maintenance, we often encountered the situation that the back-up battery's leakage lead to high current and we should pay attention to this point. Replace cable or disassemble the cell phone. High current may also be caused by cell phone cable-current short circuit. And if the back cover of the phone is the type of anti-interference and conductive, then we should notice that whether the back cover of the phone led to cell phone Short circuit.
