Although the circuit diagram of the whole machine is very complicated, it is not unattainable to learn to understand the circuit diagram. Have a certain knowledge base of electronic circuits, master a set of correct reading methods, and after learning and practicing, you can learn to read circuit diagrams. In fact, when looking at the circuit diagram of the laser disc player, you can use a variety of methods to look at the picture. In the end, we must complete several basic tasks of reading the map to achieve several basic requirements for viewing the map. Here is a discussion of the basics of looking at circuit diagrams.
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First, how to look at the laser disc machine circuit diagram
1, according to the order from large to small, from coarse to fine, the various circuit diagrams have been mentioned, CD, VCD, 
Figure 1.2.1 is a simplified block diagram of the VCD machine CD module, which is used to complete the function of the VCD machine movement, that is, to complete the function of the CD player. As can be seen from the figure, the CD module is mainly composed of circuit systems such as RF amplification, CD-DSP, servo processing and driving, and microprocessor. Among them, the RF amplifier is used to amplify and shape the RF signal to obtain various servo error signals; while the CD-DSP circuit is mainly used to demodulate the EFM data signal for error detection and correction; the servo system is used to process various servo controls. Signal; the microprocessor is the control and detection center of the above circuit, and is closely related to multiple circuits. These circuit systems are connected to other circuits through the relevant connectors (interfaces), and the main plug interfaces are T1~T5. Among them, T1 is the plug interface connected with the laser read head, T3 is the plug interface associated with the servo control mechanism (coil and motor, etc.) of the disc player, and T2 is the plug interface of the CD-DSP output signal to the VCD decompression board. On the actual circuit, these connectors may be merged or decentralized. Usually, simple letters, symbols, etc. are indicated next to the plug interface to indicate the flow direction and function of each interface signal. This is the drawing method of the typical CD module circuit diagram of the VCD machine. For beginners, how should you read this circuit diagram in 3 steps? Here is a brief explanation.
1. Intuitively start, choose the entrance, that is, look at the most intuitive and easy-to-read components and circuits at the edge of the circuit, as the entrance to the reading. A number of circuits or integrated blocks can be found by these peripheral identities along the signal line inward (possibly in the opposite direction of the signal flow).
The output of the laser head and the input end of the CD end module are connected by a plug connector, so that the rear cascade line from the laser head interface T1 should be an RF amplifier. There are 3~5 signal lines connected to the RF amplifier input through this interface. The VCD decompression plate and the CD-DSP circuit are also connected by a connector. Thus, the VCD decompression plate interface T2 to the front line (reverse signal flow direction) should be a CD-DSP circuit. The VCD decompression board interface also has a plurality of signal connection terminals, mainly LRCK, BCK, DATA and other terminals (for
There is also a host interface line), and the servo system output signal should be sent to the servo actuator to complete the servo control of the laser head. The servo actuator and the servo circuit are often connected by the interface circuit T3, but sometimes the two are directly connected. Therefore, the servo execution device interface T3 can search for the servo system against the signal flow direction, and the servo drive circuit (mainly focus, tracking, feed drive) can be found; and the spindle CLV control can be found along the signal line to the CD-DSP circuit. Circuit; In fact, the system microprocessor (usually used by the CPU) is often connected to the VCD decompression board through the data bus (some micro-processing is integrated inside the DSP chip), the interface is represented by T4, and sometimes T4 and T2 form an interface. Use the T4 interface to find the relevant pinouts for the microprocessor. The microprocessor is also connected to the keyed operation panel and the VFD display circuit, and is usually connected through the connector T5; thus, the lead pin associated with the keyboard operation and the display circuit can be found by the T5. .
2, open the gap, contact the weak link inside the circuit diagram before and after any kind of circuit diagram. The complexity and difficulty of each part of the circuit are always different, or the graphics and symbols of some components are different from the general components. These places are the internal weak links of the reading, and they are easy to read. They can be used as a picture. The internal breakthrough. You can choose these places as a breakthrough for reading the map. After opening the gap, you can quickly connect forward, backward, left, and right, and cooperate with the first method to read many circuits.
As long as the reader pays attention, there will always be many links that the reader is already familiar with inside the circuit diagram. Grasping it can quickly open the gap of the picture and develop in depth. The most intuitive and easy-to-read internal links are integrated circuits, especially those large-scale integrated circuits. They have more than 40 pins and more than 100. They are very eye-catching in the picture, and the plotters often put them. In the center or obvious position of the circuit diagram. Then, with these integrated circuits as the center, we can find many circuits. For example, the T2 interface can be found backwards from the CD-DSP chip, the RF amplifier can be found forward, and the T1 interface can be found forward. The microprocessor chip can be extended in all directions to find CD-DSP, servo system, T3 interface, T5 interface, etc. The servo signal processing chip and the RF amplifier can be found by the servo signal processing chip. It is necessary to have an integrated circuit as an internal breakthrough. It is necessary to know the specific model of these integrated circuits, know the main functions of the integrated circuit, and be familiar with the names and uses of the main pin. Otherwise, it will bring a lot of inconvenience to the reading. Sometimes the reader is already familiar with most of the integrated circuits, unfamiliar with some of its individual integrated circuits, and can guess the function of the unknown integrated circuit based on the composition block diagram and the context.
There are also some easy-to-read and easy-to-remember contents in the circuit diagram, which can also be used as a breakthrough inside the circuit. For example, the Chinese characters, foreign letters or abbreviations marked in the figure, some important and easy-to-read component graphic symbols, some adjustable resistors or potentiometers. In order to use these breakthroughs conveniently and smoothly, readers should be familiar with the physical meanings of various foreign letters and abbreviations, and have a certain foreign language foundation (usually English). Readers should be familiar with some professional terms and their abbreviations often used in audio-visual equipment. The reader should be familiar with the functions, parameters and indicators of these components. The reader's knowledge is wider, which is conducive to reading the picture. The reader should consciously remember some useful common sense.
3, difficult analysis, placed in the last two steps of the reading process, most of the circuit diagram can be understood. However, the remaining local circuits will not be understood or understood. The third step can be used to encircle the difficulties. This is the difficult part of the picture, and the last step in the picture. Readers can break through difficult circuits by various methods or means.
On the practical circuit diagram, the hard-to-understand places are often manifested in two places. One is the signal circulation process inside some integrated circuits. Since these contents are not understood, the external pin function cannot be understood. The other is a certain These peripheral discrete component circuits do not understand the purpose of setting up the circuit and do not know the signal processing process. For these difficult circuits, according to the block diagram of the whole machine, according to the functions and interconnections of each part of the circuit, through the logic analysis, the analysis function and the signal flow and other analysis methods, these difficult circuits can always be understood.
In fact, there are so many information available on the circuit diagram that you can read and use. With the reader's synthesis, analysis, and research, you can understand the whole picture. The actual situation of each person is different. The method of drawing and judging may be slightly different, and the steps of viewing the pictures are not static. The technology of laser disc player has developed rapidly. Manufacturers often develop circuits with new circuits or new functions, and even circuit programs are rather strange. On the basis of the above basic ideas of the drawing, the drawing work can be flexibly completed.
Third, look at the integrated circuit diagram method and requirements <br> Laser disc player uses a variety of models, functional integrated circuits (IC), and several large-scale or very large-scale integrated circuits as the core, with other integrated circuits and discrete components , constitute the whole machine circuit. These core integrated circuits can contain the functionality of one or several system circuits. Looking at the whole circuit diagram, block circuit diagram and system circuit diagram are all looking at the circuit diagram with the integrated circuit as the core. How should I look at the integrated circuit diagram? What to see? What requirements should be met? The following is a brief description.
1. The method and content of looking at the integrated circuit diagram. The method of looking at the integrated circuit diagram can be carried out by using the above three sentences and three steps. Alternatively, the integrated circuit can be used as the center, and the signal path outside the block can be connected and expanded outside the block. Then establish the connection between the various integration blocks, and finally grasp the global and the details; it can also be combined with several methods, and the picture can be viewed according to the drawings.
When looking at the integrated circuit diagram, what should be mainly viewed? Can be summarized into the following four sentences: function type, signal flow, internal and external contact, pin function. Explained separately below.
(1) The type of function must first understand the type, type and main functions of the integrated circuit used. This is the first step in reading the integrated circuit. For example, the types of integrated blocks used in CD players mainly include RF amplifiers, servo signal processing and digital signal demodulation circuits, servo drives, system controllers (generally integrated in DSP integrated circuits), and the like. First of all, it is necessary to know the specific model of the integrated circuit, and to understand the type of the integrated circuit, especially to familiarize with its main functions. The main functions and circuit structures of different types of integrated circuits may be similar; the circuit structure and circuit program may be different, but the same functions can be accomplished. Familiarity with the function is the most important.
In order to quickly and correctly read the circuit diagram, the reader should consciously accumulate relevant information of some common integrated circuits, purposefully remember the specific models and types of some integrated circuits, and understand the general trends and latest developments of using integrated circuits. Some integrated circuits have different models, but the functions are the same, and can even be used directly by each other; some blocks have similar serial numbers, but the functions and pinouts are completely different; some integrated circuits that appear later can complete the functions of several early integrated blocks. After the readers have mastered the information, they will show great advantages when reading the integrated circuit diagram. Tables 2, 3, 4, and 5 list the common integrated block models, functions, and reference voltages of some laser disc players in our company, which can be seen by the reader when viewing the drawings.
(2) Signal flow When reading a circuit diagram, it should not be satisfied to only grasp the type and basic functions of the integrated circuit, and should be familiar with the basic processing of the signal. Usually, the structure of the internal circuit of the integrated block is very complicated. The reader does not need to do a detailed analysis of it, but should be familiar with the signal processing of the internal circuit, or should understand the internal functional block diagram. The flow chart of the signal can be seen from the block diagram, and it can be seen which specific functions can be completed by the integrated block. The integrated circuit can be regarded as a component, and it is not necessary to pursue the structure and detailed working process of the component too much, but it should clarify the specific functions completed by each block in the integrated circuit, that is, familiar with the input and output signals, and familiar with the waveform amplitude of the signal. , the law of frequency changes, familiar with the connection between the various boxes, familiar with the ins and outs of the signal in the integrated block. At this point, it is a preliminary understanding of the integrated circuit diagram.
At present, some of the circuit diagram information of the whole machine is not comprehensive enough. Only the number of pins of the integrated block and the symbols of each pin are given. The internal block diagram of the integrated block is not given, and the DC operating point of the pin of the integrated block is not given. It will bring inconvenience to the in-depth reading of the map, the reader should look for some other information to make up for its shortcomings. Also, many internal component block diagrams are often labeled with foreign letters or abbreviations, and it is also difficult for beginners to come. This requires the reader to be familiar with the Chinese meaning of letters and abbreviations as soon as possible, otherwise it is difficult to read these circuit diagrams.
(3) Internal and external contact Due to the characteristics of the integrated process, the integrated circuit must be connected to the peripheral components through the pinout. In order for the integrated circuit to perform certain functions, it must be associated with external unit circuits or components, and must also be connected to the pre-stage and post-stage circuits through the pinouts. When reading a circuit diagram, the circuits inside and outside the integrated circuit must be connected, and they are used as a whole of the circuit system to perform certain functions. Can not contact the internal and external circuits, will not see the ins and outs of the signal, it is difficult to analyze the function of the circuit.
For the same integrated circuit, in the hands of different machine designers, different external circuits may be designed to match different component networks. Since the external discrete circuit can be varied, these discrete circuits are often difficult circuits for reading pictures. It takes some effort to break through these difficulties, otherwise it will not be able to fully and correctly read the whole circuit diagram.
(4) Pin function On the integrated circuit diagram, each pin not only needs to be marked with a sequence number, but also its name is indicated by a simple letter symbol. These alphabetic symbols are often abbreviations in English and can represent the function of the pin. When looking at the integrated circuit diagram, we must pay great attention to the function of each pin. The lead pin is the link between the internal and external circuits. It is necessary to clarify the connection between each pin and the internal functional block diagram. It is the pinout of the corresponding internal frame; it is also necessary to explicitly take the function of the pin external component, and the external circuit is matched by the pin. The internal circuit works. Some pinouts are the input and output ports of an integrated circuit. These pinouts are important when looking at the circuit diagram. When reading the integrated circuit diagram, it is necessary to observe the individual block diagrams representing the internal functions one by one, and also identify the corresponding pinouts at the same time, and identify the external circuits or components. These tasks are often the main work of reading the integrated circuit diagram.
Generally, integrated circuit leads and external components have certain regularity, but the law is not static. In some models, some pins are not used, or the signal flow is different, and the reader should be flexible.
2, read the lead to make "four clear"
Reading the pin is a regular and important task in reading the integrated circuit diagram. Familiar with the internal composition block diagram, can deepen the understanding of the function of the pin-out foot; familiar with the function of the pin-out foot can enhance the understanding of the block diagram. When reading the lead, the following "four clear" should be made.
(1) Symbol function According to the original designer's requirements, each pin has its own purpose and name. According to the design idea of ​​each pin, English letters or abbreviations are marked near each foot. Professionals or maintenance personnel can know the nature and function of the foot according to the English words marked on the drawings. However, it should be noted that different manufacturers may use different abbreviations for the same nature and function; in most countries, manufacturers use the same or similar abbreviations. Common notation: RFO means high frequency (EFM to be demodulated signal) output, RCIN means remote control signal input, BCK means data clock signal pin, RLCK means left and right channel clock signal pin, FOK means focus completion signal Lead pin, DATA indicates the data signal pin, CLK indicates the clock signal pin, FE indicates the focus error signal pin, TE indicates the tracking error signal pin, G indicates the green primary signal pin, and HSYNC indicates the line sync signal pin. VSYNC represents the field sync signal pin, NC represents the idle standby pin, GND represents the ground, and so on. If the reader is very familiar with these word representations, it will bring great convenience to the view of the integrated circuit diagram. If you are not familiar with these words, it will cause many difficulties for viewing the pictures.
(2) Signal waveforms Many pinouts are input and output signal ports. Some pinouts are switch or pulse signals, data streams or analog signal ports, and some pinouts are critical test pins. The reader should be familiar with the signal waveforms of some important pinouts, understand the shape, amplitude and frequency of the signal waveform of the pinout, which is of great significance for reading the circuit diagram and troubleshooting the whole machine. Usually, an oscilloscope can accurately read the input and output waveform shape, frequency and amplitude of the pin.
(3) The relevant data should also be familiar with the relevant data of the lead. It is also important for reading circuit diagrams and troubleshooting faults. First, be familiar with the data about the signal waveform, and be clear about the range of the signal amplitude and the frequency value of the signal. Secondly, you should be familiar with the data of the current, voltage, and resistance of the pin, especially the static working voltage and dynamic working voltage of the pin. For those pins whose dynamic and static DC voltage values ​​are not the same, more attention should be paid.
(4) The flow direction is clear. It is also necessary to pay attention to the flow direction of the pin signal. It is necessary to distinguish the name of the foot signal, and distinguish whether the foot is a signal input terminal, a signal output terminal, or a bidirectional signal (I/O) port. If the signal flow is not clear, the circuit diagram will not be understood. Some pinouts are signal control terminals, while CD-DSP, servo circuits, and VCD decompression are required to set the control signal output and input. The control signal may be a switching voltage, a data stream, or a PWM signal.
Second, look at the basic method and main content of the unit circuit diagram <br> Each system circuit is composed of several unit circuits. In order to understand the whole circuit, the block circuit and the system circuit, you must read the unit circuit diagram of each system. The unit circuit is the circuit unit of the whole machine. As the level of integrated circuit technology increases, several or even dozens of unit circuits can be integrated into one integrated circuit. At present, on the whole circuit diagram, there are fewer and fewer discrete unit circuits, which makes the task of analyzing the unit circuit in the whole machine less and less, and it is easy. However, it is very familiar with the function principle of the various unit circuits of the whole machine. It is very necessary for mastering the working principle of the disc player and for repairing the disc player.
When reading the unit circuit diagram, you should mainly read the following contents: principle, function, structure, type, transformation process, numerical waveform.
1. Principle and function Each circuit system must complete a signal processing function, and each unit circuit only completes a certain part of the signal processing process. When reading the unit circuit, first understand the purpose and function of the unit circuit in the circuit system, and what tasks it mainly accomplishes. Then, according to the function and task requirements, analyze the working principle of the circuit. Sometimes the function and function of the unit circuit are difficult to determine immediately. The basic function of the unit circuit can be assumed based on its position in the system circuit, and its working principle is analyzed, then analyzed and verified, and finally determined.
The verification and verification work is mainly realized by oscilloscope detection. Analysis of the working principle of the circuit requires knowledge of the reader's theoretical basis and reading experience. The principle of analysis mainly refers to clarifying the content and characteristics of the circuit signal, how the circuit generates new signals and how to implement signal transformation.
2. Structure and type When analyzing circuit functions and principles, it is inevitably accompanied by the structure and type of the analysis unit circuit. For the integrated unit circuit, the specific form of the circuit can be omitted; for the discrete part circuit, the circuit structure must be analyzed in order to correctly analyze the circuit type and working principle. It should be noted that the unit circuits that perform the same function can use circuits of different structures and types; even circuits that implement the same function can use circuits with different working principles. For example, in a CD player or a VCD disc player circuit, correcting errors and error codes is an important issue. In order to accomplish this task, circuits of different principles can be used; different methods can be used to correct bit errors and error codes; different structures and Types of circuits implement error correction; until now, people continue to study more effective error correction measures.
3. The transformation process analyzes the working principle of the circuit, which is inevitably accompanied by the transformation process of the analysis signal. Analysis of the transformation law of the signal is the key to analyzing the circuit principle. The signal analysis is clear, and the working principle must be solved. The analysis signal mainly analyzes the waveform, amplitude and frequency of the input signal and the output signal, analyzes their contents and characteristics, and analyzes the principle and function of the signal transformation.
4. Values ​​and waveforms When analyzing signals, you should be familiar with the laws of signal waveforms and should be familiar with their values. The amplitude and frequency of the signal are also important contents reflecting the characteristics and laws of the signal. By analyzing the waveform variation law of the input and output signals, and analyzing the signal amplitude and frequency variation law, the working principle of the circuit can be deeply grasped. In addition, for the discrete component circuit, the DC operating point value of the circuit is also the content of the analysis, which directly affects the working state and working principle of the circuit; for the integrated circuit, the dynamic and static operating voltage values ​​of the corresponding lead-out pins are also We must pay great attention to it.
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