Most of the big screen color TVs nowadays are I2C bus color TVs. Once the faults occur, the previous experience and ideas of maintenance are often not used: First, the I2C bus color TV often appears to be contrary to the conventional failure phenomenon, and it is impossible to repair the repair; second is not Know how to judge whether the I2C bus system is normal; third, do not know how to replace the CPU and memory. In fact, as long as everyone breaks through these three points, the maintenance of the I2C bus color TV will be solved.
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I. Judging method of I2C bus color TV Many maintenance personnel only need to see the words "SDA" and "SCL" on the CPU, they think that this machine is I2C bus color TV, but it is not, CPU
The words "SDA" and "SCL" are marked on the CPU, only the I2C bus is introduced on the CPU. However, whether the manufacturer has developed the bus control function depends on what circuit is hung on the bus. If the memory and small signal processor are both on the bus, the machine is an I2C bus color TV. When repairing such a color TV, it is necessary to follow the inspection features of the I2C bus color TV. What we usually call the I2C bus color TV refers to this category. If one of the memory and the small signal processor is not hung on the bus, it will not be a real I2C bus color TV. When repairing such a color TV, it will still be processed according to the old method.
Second, I2C bus color TV fault self-test
Because the I2C bus system is a microcomputer system that combines hardware and software, it can perform self-test on system faults and display test results, providing self-check information for maintenance personnel. Maintenance personnel can judge faults by analyzing fault information. The approximate location and nature of the fault. At present, the display mode of color TV self-checking information is as follows.
1, the indicator display mode
When the CPU detects that the system is faulty, it lights up the indicator light and the maintenance personnel can judge the fault location according to the blinking rule of the indicator light. For example: Sony Guixiang series color TV (KV-ES29M90, KV-EFM90, etc.) use this method. When the CPU detects that a controlled device is faulty, it enters the bus protection state, and the whole machine has three. At this time, the indicator light on the panel flashes. The maintenance personnel can judge the fault location according to the number of flashes of the indicator light. The details are shown in the following table.
2, the screen display mode
When the CPU detects that the controlled circuit is faulty, the fault location and the fault property are displayed on the screen by characters, and the maintenance personnel can judge the fault property according to the displayed result. For example, Changhong G2966 color TV adopts this method. When the screen displays SDA_GND or SCL-GND, it indicates that the bus is shorted to ground.
3, fault code display mode
When the CPU detects that the bus system is faulty, it displays the screen in the form of a code, and the maintenance personnel can judge the fault location according to the fault code. For example, the Philips MD1.0A movement uses this method. After each power-on, the CPU detects the relevant circuits in the system through the I2C bus and displays the test results in digital code. The maintenance personnel can display the numbers according to the displayed numbers. Code to determine the fault location.
Third, I2C bus color TV special fault phenomenon 1, bus protection Bus protection is a special phenomenon of I2C bus color TV. When the CPU
When it is detected that there is a serious problem in the system (such as bus short circuit, output port and power open circuit, etc.), the CPU will execute the bus protection program, and the system enters the protection state. At this time, the color TV may have some special failure phenomena, for example, it cannot be turned on. White net grating, button failure, black screen phenomenon, power relay "å—’å—’" ringing. Therefore, when encountering these phenomena, firstly, it can be processed according to common faults. If the fault point cannot be found, the conversion idea is checked to see if the bus system is abnormal and the bus system is abnormal and the bus protection is caused. After the conversion idea, Sometimes it's easy to find the fault. The following table lists the possible failures caused by damage to some components in the color TV and I2C bus color TV.
As can be seen from the above table, when any one of the controlled devices on the I2C bus is damaged, the system may enter the bus protection state, causing a malfunction that is illegal. This should cause the maintenance personnel to pay attention to it. .
2, software error
The fault phenomenon caused by software error is another special phenomenon of I2C bus color TV. In ordinary remote control color TV, the function that a color TV can realize is only related to the circuit used by this color TV. For example, there is a two-way AV in the circuit. The input circuit determines that the machine has two AV input functions, but in the I2C bus color TV, the functions that the color TV can achieve are not only related to the circuit (hardware), that is, the existence of the hardware circuit must correspond to the setting of the software data, otherwise Even if there is a two-way AV input circuit, it does not necessarily have a two-way AV
Input function. Maintenance personnel often encounter such a situation. Sometimes when the TV fails, all the circuits are found and no fault can be found. However, after checking the software, the problem is immediately found.
Four, noteworthy pins
Many I2C bus color TVs have special function pins on the CPU and the controller. The voltage of these pins has a great influence on the control function of the I2C bus. Only when the voltage of these pins is normal, the I2C bus system can normal work.
1, I2C bus on/off control pin on the CPU
The I2C bus on/off control pin is set by the manufacturer for easy debugging (or testing). Under normal circumstances, the pin is high, the CPU has bus control, and data can be transmitted over the bus. When the pin goes low, the CPU no longer has control of the I2C bus, and it gives control to the debug computer management on the production line. Therefore, when the voltage of the foot is abnormal, the TV may enter the factory debugging state. This pin is often represented by symbols such as “FACTORYâ€, “BUSOFFIN†or “BUSON/OFFâ€.
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