Some basic methods for reading mobile phone circuit diagrams

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Some basic methods for reading mobile phone circuit diagrams [Copy link]

Many students and colleagues have reported that they have replaced all the components of a faulty mobile phone, but the phone still cannot be repaired. In most cases, they do not have a thorough understanding of the mobile phone circuit and cannot read and analyze the mobile phone circuit diagram. "One blow, two wash, and three replace" can certainly solve some problems, but if you go deeper, you will be helpless. Many people get a headache when they see the circuit diagram, feel that they have no clue and cannot start. In fact, the mobile phone circuit diagram has a strong regularity. Let's talk about some basic methods of reading mobile phone circuit diagrams.
· Mastering the location, function, characteristics and technical indicators of the main components and understanding their functions can help us understand the guiding ideology and layout of the circuit diagram. In addition, pay attention to the components on the circuit diagram, block diagram, and component distribution diagram. If necessary, combine the physical board diagrams with each other for verification and analysis. Also, pay attention to the positive and negative poles of the components cannot be connected in the opposite direction. For example, the symbol of the diode system has a triangle on the left and a short bar on the right. The lead on one side of the triangle is the positive pole, and the lead on the side of the short bar represents the negative pole. The electrodes of triodes and field effect tubes, and the correct order of the steps of integrated ICs should not be connected incorrectly. During maintenance, you should also avoid connecting places that should not be connected together. If there is a place where the "+" symbol is not connected, it cannot be connected together. Pay special attention when flying wires.
· Break the whole into parts The overall schematic diagram can be divided into several parts. For example, when analyzing the working principle of the RF part, we often analyze it from the aspects of the receiving part, the transmitting part, and the frequency synthesizer circuit. This part of the circuit can be subdivided into many branch circuits. In the process of subdivision, if some individual components or principles are difficult to understand, they can be put aside for research. In this step, we only seek to clarify the main modules and components of each part. Connection and function.
· Comprehensive analysis That is, the various components are integrated. Connect from the input end of the overall circuit diagram to the output end, and observe how the electrical signal is transmitted and amplified step by step in the circuit.
Comparative analysis For each basic unit circuit, find out the DC path, AC path and feedback path in it to determine whether the static bias of the circuit is appropriate, whether the AC signal is amplified and transmitted properly, and what kind of filtering the derived signal undergoes. Otherwise, short circuits will cause other faults. Be familiar with the characteristics of various basic circuits. For example, you should remember and analyze thoroughly the basic circuits such as various amplification, oscillation, detection or phase-locked loops, so that it will be easy to read circuit diagrams in the future. For example, the working principles of the L2000 series mobile phones and the V998 series are roughly the same. When analyzing the circuit diagram of one of the models, you can also compare its main mobile phone circuits. In this way, you can get twice the result with half the effort. For the newly launched TAICHI series mobile phones, P2K mobile phones, etc., combine the analysis of their evolution process to achieve the ability to respond to changes with constancy. For the same type of integrated IC, in addition to comparing its efficacy in the same brand series circuit, it should also be compared with other brands and models to analyze their similarities and differences, because modern mobile phone models are launched in an endless stream, with many different functions, but the specifications are always close to GSM specifications, and the working principles of the basic circuits are roughly the same. By doing the above work, you can draw inferences about other situations and respond quickly to the dazzling and ever-changing failures of mobile phones.
· Index estimation In order to have a deeper understanding of the circuit diagram, some major technical indicators can be estimated to obtain a quantitative concept of the technical performance of the circuit, and the functions of each component and the electrical parameters of the pins should be mastered. If necessary, instruments should be used to verify, and the accuracy of the circuit diagram should be questioned with facts. Because some drawings in maintenance books are not original drawings.
The above methods are more suitable for the working circuit of the RF part of the mobile phone. For the working circuit of the logic part, we should grasp the following points:
· Power supply circuit: analyze how the power supply combines with the chip, component display screen, etc. to supply power;
· Clock circuit: analyze the clock drive circuit, which pin of the integrated IC is specifically connected to;
· Reset circuit: that is, analyze which pin of the integrated IC is RESET specifically connected to;
· SIM card holder, keyboard, microphone input path, generally their input path is more prone to problems;
· Display screen, background light, indicator light, ringing/earpiece output path.
Of course, when analyzing the logic part circuit, we must first understand the basic characteristics and functions of each major integrated IC. Such as: central processing unit, code chip, font library, audio module, etc. Through the above analysis, we can grasp their intrinsic connection and control essence. The above methods are not fixed, nor are they suitable for all mobile phone circuits. Sometimes the methods are not clearly defined and can be performed interchangeably or in the reverse order. They should be used flexibly according to actual conditions.

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wklwklwbh

Thank you very much for your selfless sharing of knowledge. I have benefited a lot from it. I am really grateful!

xihosi

Thank you very much for your selfless sharing of knowledge. I have benefited a lot from it. I am really grateful!