Summary: The electron vocational students, the main purpose is to develop an electronic professional skills, that is, for a variety of electronic equipment for maintenance, repair, make it work. In this paper, in order to repair the TV as an example, to talk about their professional skills to improve the electronic paper some ideas Keywords: improve, electronics, operating, electronic learning professional skills, the main purpose is to develop an electronic professional skills, that is, for a variety of electronic equipment for maintenance, repair, make it work. Now TV's overhaul as an example, to talk about their professional skills to enhance the electron some of the views.
TV is a more complicated home electronics products, not only for the TV repair professional systems need to understand the basics, as well as flexible use of this expertise, but also a skilled operational skills. It can be said, is the brains of the TV repair process in close coordination with the hands is the high degree of unity of theory and practice. TV repair skills improve, you can proceed from the following aspects.
First, to have a more solid theoretical foundation of theoretical knowledge to master circuit television is very important, which is the basis for circuit failure analysis, without this foundation, all of the analysis, inference can not really carried out, but only wild speculation. For TV master theory, first block diagram of the control circuit, followed by memorizing the circuit schematic, understand how it works, works. Block diagram of the TV master is to memorize the TV from the power supply, tuner circuits, small signal processing circuit, an audio processing circuit, horizontal and vertical scanning circuit, CPU control circuit, etc., to understand the working relationship between the various parts. Block diagram of the circuit memorized, can help us to grasp the whole circuit works to help us understand the specific circuit diagram, even if some of the more unfamiliar, local circuit difficult to understand, if we block diagram of the circuit from the point of view , learned that this circuit should belong to which part, then we in the analysis of this circuit, it will be assumed that within a range, analysis, inference, which is not prone to bias.
Secondly, to memorize the circuit schematic, this memorize To understand the circuit works performed memorization process on the basis of work. See circuit diagram, the first overall look, a glance, with block diagram of the circuit of view. (A), the block diagram of each circuit block diagram and schematic circuit corresponding to find out, and then each of the core elements of the circuit to find out. (B), each part of the circuit by a switching power supply, secondary power supply direct-current power lines marked out on the circuit diagram, because all electronics are inseparable from the DC power supply. (Iii) the change in signal flow marked out on the circuit schematic. The television signal input from the antenna to the tuner, IF signal after the mixer output becomes fixed, and then sent to the small signal processing circuit into R, G, B three primary color signals, supplied to the discharge tube shown magnified image; in addition, then the sound signal to the audio amplifier circuit. Again, coming from the washer into the video and audio signals, and how, after the switch again to display the picture and sound. (D), various loss voltage, the voltage is too high or overcurrent protection caused by the process marked out. Such as a short circuit caused by the breakdown line pipe, beam current is too large, and the + B voltage increases, the manifold caused damage protection. (V) and the reaction process signals received by the CPU panel buttons or the remote control signal caused marked out. Such as channel selection, shutdown, adjust the volume, adjust the brightness, color, mute, and no signal is automatically shut down, and so on. Read the above content, then the course of our work on television is already an idea. Look at the fine aspects, such as the function of each pin televisions manifold, when the magnitude of the voltage of the work, its role in the external circuit, and the like; each part of discrete components circuit diagram parameters, the role of each member; as TV in line excitation, the role of the line output circuit of each component and the like. These require more to find information, more reading before mastering it. But reading circuit is not a one-step thing, but to continue to read, read again and again, this is a process of deepening understanding.
Second, understand the board understand the circuit board is also the basis for circuit maintenance effort, a specific circuit board than the circuit diagram is much more complicated, the main components are placed no law, those copper wire winding, etc. etc., but you must understand the circuit board, otherwise I do not know the specific operation where to start. To understand the circuit board, in essence, the circuit diagram of each component on the circuit board to find out the corresponding position. How to read the board do? First, the overall layout of the television board to understand. For example, the power part arranged in the upper left corner of the board, line scan in the lower left part of the arrangement, that is part of a large voltage high current circuits rely on relatively recent. LNB part of the circuit arrangement in the lower right corner, so on the one hand to facilitate access to external antenna, on the other hand is also away from high-current power supply circuit and line circuits to avoid weak TV signal interference. Another example is the remote control receiver arranged in the vicinity of the panel, which also makes handling the remote control signal, CPU panel signal is arranged above the circuit board and the moderate right-hand side. Small-signal processing integrated circuits are arranged in the vicinity of the tuner and so on. Understanding these laws helps us read the board. Second, the board should be read from coarse to fine, and global to local. The first part of the circuit in each of the key components, easily recognizable device to find out, in order to determine the approximate location of this part of the circuit. For example, part of the switching power supply switch, filter capacitor, switching transformer, the transformer secondary rectifier diodes; line scan circuit line pipe, flyback capacitor, ignition coil, line excitation transistor, line excitation transformer; high-frequency, small signal processing Manifold, CPU manifold and so on. These devices are easy to find out, to find out after the position corresponding to the circuit to determine it big; then every part of the circuit to find out those auxiliary components, it is not a very difficult thing, because every part of the circuit components quite together, which in the vicinity of those critical components. In addition, they still have a label, such as the power part of the resistance, with the R511, R512, R513 represents the like. Finally, the power that the DC power supply, the key change signal flow is directed through the pin components on the circuit board to find out. Find the key to the board, or memorize the circuit diagram.
Third, the experimental work of this step of the circuit, in essence, verification of circuit theory. After all, practice is the sole criterion for testing truth, but for circuit analysis, various discussions or arguments, has not been proved in before, we should also be skeptical of this judgment, it can not as a fact of truth, this is the a rigorous scientific approach. For example, in order to deepen the understanding of the power section, the line can slip off, connected to dummy load, boot, and then measuring the voltage of each point, waveforms. Again, start by disconnecting the resistor feedback network, and then boot, verify that the switching power supply does not vibrate like. Another example is with a remote control switch machine experiments to Sanyo movement, for example, by analyzing the circuit diagram can be found, the remote boot process is this: the remote control receiver connected to the signal emitted after the CPU from the control pin send a low level, the transistor V1 of the b pole, so that this transistor is turned off, so it c voltage electrode is kept on 5V, and is added to the b pole triode V2, the transistor guide portions through two power regulators, giving the small-signal integrated circuits, power supply IC field, so field scanning circuit is working properly, the shutdown process is just the opposite. According to The Principle, if V1 is c, e Breakdown damaged, TV will not turn on, if V2 of c, e Breakdown damaged, you can not shut down. According to the theoretical analysis, we can produce these faults to verify, as with the wire V1 of c, e pole short circuit, then power, verify that really can not remote boot. Further, the analysis from the circuit, where there are problems, will lead to the emergence of the phenomenon can not boot. Such as remote control, receiver, receiver and the line between the CPU, CPU manifold and other problems, power supply CPU manifold, reset, crystal and other problems, may result in not normally switch machine. Another 11 to do an experiment on these analyzes, and the results compared with the theoretical analysis. Through these experiments, we will in this part of the circuit has an intuitive and profound understanding. If the television each part of the circuit are verified by experiments, then we will have a complete circuit of television and profound understanding of the theoretical understanding increased by one level. But in doing circuit experiment, you must pay strict attention to safety and personal safety circuits because these circuits experiments relate to disconnect certain components, or disconnect a part of the circuit, the operation, they have to go through analysis, feasibility demonstration, especially in the large voltage switching power supplies and line scan part of a large current circuit. As the peak switch coil parallel snubber capacitor switching power supply is not disconnected; line scan circuit inverse heavy drive capacitance is not broken; line branch off to pick up a dummy load, and so on.
Fourth, maintenance practices through all aspects of previous training, we have a deeper understanding of the television, the practice has been to repair and laid a solid foundation, but must maintain the practice of this ring, will really understand circuit theory, learn to use theoretical knowledge to analyze real problems to solve practical problems.
Overhaul of the TV for a certain kind of symptoms, you should first use a circuit block diagram of the television set is analyzed to determine which part of the circuit there is a problem; then analyzed according to the circuit diagram, and gradually narrow the scope of failure, until you find faulty components. In analyzing the failure phenomenon, this idea of the whole to part must be strictly adhered to. For example, there is grating, no image, no sound of failure; block diagram of the circuit according to the analysis, there is a grating, the power supply circuit, horizontal and vertical scanning circuit certainly working properly; no image, then the tuner, the amplifier circuit, small signal processing circuit, depending on the circuit might not normal; no sound, then the tuner, the amplifier circuit, small signal processing circuit, audio amplifier circuit may not properly. Because no image, no sound simultaneously, then it should be tuner, the amplifier circuit, small signal processing circuit and other public channel a greater chance of failure. Again, there are sound, with only a horizontal bright line fault on the screen; there is sound, then the tuner, the amplifier circuit, small signal processing circuit, audio amplifier circuit are normal; a horizontal bright line appears on the screen, Description power supply circuit, line scan circuit certainly work, but the issue should be present scanning circuit. But now with the development of bus technology, the development of the switching power supply protection circuit, the difficulty of the faulty portion of the judgment increased. For example, before the integration of field work the TV is not normal, manifested symptom is a horizontal bright line, but then the use of bus protection technology, Symptom manifestations is 'three noes' to protect shutdown. Any contact with the CPU data have manifold there is a problem, when the CPU detects that it does not work, it will send a signal of the switching power supply protection shutdown, which would cover the real Symptom up, increasing the difficulty of judging. This requires careful analysis, to lift the protection, showing that the real fault phenomenon, coupled with the judge. This must be done to protect the whole circuit process have a deep understanding.
After determining which part of the fault circuit, and then determine the problem in this part of the circuit which level. For example, switching power supply + B voltage is 0V, the switching power supply can be divided into smaller parts, such as the rectifier filter circuit, amplifier circuit, a positive feedback circuit, the other over-current protection circuit, voltage regulator circuit; which part of a problem , may lead to the switching power supply is not working properly. This would be in accordance with the circuit diagram for television in switching power supply section, the detailed analysis, we concluded that a variety of possible causes, and to develop the corresponding simple and feasible verification program, to be verified until you find the faulty element so far. In short, in the search for what part of the terms of other large fault blocks and failures, we must stay calm and give full play to the theoretical knowledge learned, careful analysis of the scrutiny, and by simply measuring the voltage waveforms to determine; in Looking faulty components, apart from the calm, also emphasize work carefully, skilled movements, because the process may have to disassemble components, switch machine measurement, the slightest negligence, it is easy to have an accident.
After each maintenance practices, but also pay attention to write maintenance records, maintenance write summary, to symptoms, their own analysis and judgment, maintenance of the program, the results of the implementation of maintenance programs and data for various measurements, some unexpected circumstances write it down. Summed up from the practice of some regular things, the practice and theory through.
Fifth, look at electronic magazines, absorb maintenance experience of others in addition to their own maintenance practice, thinking, usually have to look at 'electronic newspaper', 'home repair', 'Electronic World' magazine, watch out for other maintenance personnel Maintenance cases encountered, which broaden their horizons and extend maintenance ideas. This is a very important aspect. Because, after all, their own personal practice is limited, experience is limited, must absorb the experience of others, to stand on the shoulders of others. But without their own hands, their own experience, the experience of others is not absorbed, and this point is important to note.
If we continue to strive from the above five aspects, then we can gradually increase our ability to access the circuit.
References Chen Jin Sen, 'appliance repair base'