One of the most common types of TV failures is the fact that TVs cannot be turned on. Take Skyworth TVs, which are currently widely concerned by users, there are several main reasons why they cannot boot: What kind of detection methods can be used to judge? ?
First, power failure
1, the indicator light but unstable
Detection method: Explain that the 5V standby voltage is abnormal, the 5V voltage measured by the meter is only about 3V, and unstable. Then start to check the IC12's peripheral and feedback voltage regulator circuit. After checking, no abnormality is found. Replace IC12. The fault still remains unchanged. The standby circuit outputs a total of 2 groups of voltages. One group is 5V. One group is 30V. Then the 30V output is disconnected. 5V is returned to normal. That means 30V There is a problem. The measured D30 has been softly broken down. LCD TV troubleshooting.
2, found that the indicator light is not bright after boot
Detection method: Suspect the problem is in the standby circuit or the previous stage. Measuring the voltage of the 300V capacitor is only about 300V, indicating that the PFC circuit does not work. The power supply for the standby circuit is also measured. There is no power supply output for 5V and PFC. The problem should be in the standby circuit. The voltage of the standby IC is also not abnormal. Substituting the IC is also not good. There is no problem in measuring R96 and Q13. Later, it was not intended that D23 found that it had been broken down, and that the replacement LCD TV had resumed normal work.
3, open the cover and found that the power insurance burned
Detection methods: Further testing found D1 IN5406 and Q7 K2837 of the PFC circuit. Under normal circumstances, the replacement of the above components can be repaired. However, sometimes the above components will be bad and the bad bridges of successive generations will be bad after the continuous generation of Z6 180V regulators. If there is no 180V voltage regulator on hand, in case of emergency, the Q6 wire can be directly connected with the Q6 wire and the LCD TV can resume normal operation.
Second, part of the line failure
The failure of the line section mainly includes the following three possibilities.
1, is not part of the line;
2. The power supply cannot work properly if the X-ray protection or over-voltage, over-current protection and excessive current are caused by abnormal operation of the line;
3, is part of the line has been working, but the line output transformer power supply circuit is poor and the whole three-none;
Detection method: If the power supply is normal and the line is not working, first check whether the line pushing the collector voltage is normal, then check the output line of the line. Normally, the inspection line should be placed on the output transformer and its periphery.
If the line pushing the collector voltage is not normal, first eliminate the failure of the pusher itself, and then repair the line oscillation circuit. It is common to start the power supply resistor to open the circuit. For the three nothings caused by the action of the protection circuit, first determine what protection action is taken.
The method is to disconnect the protection branches one by one and check them separately. X-ray protection or overvoltage protection should focus on checking whether the line frequency is too low and whether the line retrace capacitance is too small. For overcurrent protection or current overpowering of the ambassador, the line output transformer and its load circuit should be checked.
As for the case where the line has been working but the three are relatively simple, it is mainly to check whether the high voltage, medium voltage and low voltage power supply circuits are normal and whether the filament power supply is normal. This is often referred to as a "black screen."
Third, component failure
In general, overpressure or over-current phenomena can be certain.
Detection method: The focus of inspections should first eliminate excess pressure or short circuit, and then make other repairs.
Due to the different models, there are other factors that affect the normal startup. Then the following detection methods come in handy.
When the microprocessor (CPU), memory, program memory, and I/O integrated circuit operating power supply are all normal, they cannot be turned on. When further inspections are performed, the software should be used. First replace the user memory using substitution method (usually 24C16, 24C32, 24C64 and other models), if the fault still exists, under certain conditions, you can try to upgrade the FLASH program memory.
If you do not have the upgrade conditions, you can also use the oscilloscope to measure the transition of the SDA and SCL bus voltages of the memory at the instant of power-on to determine the fault location. In general, the main reasons for the non-booting are the normal operating conditions of the microprocessor (including the power supply, reset signal, crystal oscillation signal, memory communication signal, SDA/SCL signal, FLASH program memory communication signal), and user memory. Working conditions, working conditions of FLASH memory.
First, power failure
1, the indicator light but unstable
Detection method: Explain that the 5V standby voltage is abnormal, the 5V voltage measured by the meter is only about 3V, and unstable. Then start to check the IC12's peripheral and feedback voltage regulator circuit. After checking, no abnormality is found. Replace IC12. The fault still remains unchanged. The standby circuit outputs a total of 2 groups of voltages. One group is 5V. One group is 30V. Then the 30V output is disconnected. 5V is returned to normal. That means 30V There is a problem. The measured D30 has been softly broken down. LCD TV troubleshooting.
2, found that the indicator light is not bright after boot
Detection method: Suspect the problem is in the standby circuit or the previous stage. Measuring the voltage of the 300V capacitor is only about 300V, indicating that the PFC circuit does not work. The power supply for the standby circuit is also measured. There is no power supply output for 5V and PFC. The problem should be in the standby circuit. The voltage of the standby IC is also not abnormal. Substituting the IC is also not good. There is no problem in measuring R96 and Q13. Later, it was not intended that D23 found that it had been broken down, and that the replacement LCD TV had resumed normal work.
3, open the cover and found that the power insurance burned
Detection methods: Further testing found D1 IN5406 and Q7 K2837 of the PFC circuit. Under normal circumstances, the replacement of the above components can be repaired. However, sometimes the above components will be bad and the bad bridges of successive generations will be bad after the continuous generation of Z6 180V regulators. If there is no 180V voltage regulator on hand, in case of emergency, the Q6 wire can be directly connected with the Q6 wire and the LCD TV can resume normal operation.
Second, part of the line failure
The failure of the line section mainly includes the following three possibilities.
1, is not part of the line;
2. The power supply cannot work properly if the X-ray protection or over-voltage, over-current protection and excessive current are caused by abnormal operation of the line;
3, is part of the line has been working, but the line output transformer power supply circuit is poor and the whole three-none;
Detection method: If the power supply is normal and the line is not working, first check whether the line pushing the collector voltage is normal, then check the output line of the line. Normally, the inspection line should be placed on the output transformer and its periphery.
If the line pushing the collector voltage is not normal, first eliminate the failure of the pusher itself, and then repair the line oscillation circuit. It is common to start the power supply resistor to open the circuit. For the three nothings caused by the action of the protection circuit, first determine what protection action is taken.
The method is to disconnect the protection branches one by one and check them separately. X-ray protection or overvoltage protection should focus on checking whether the line frequency is too low and whether the line retrace capacitance is too small. For overcurrent protection or current overpowering of the ambassador, the line output transformer and its load circuit should be checked.
As for the case where the line has been working but the three are relatively simple, it is mainly to check whether the high voltage, medium voltage and low voltage power supply circuits are normal and whether the filament power supply is normal. This is often referred to as a "black screen."
Third, component failure
In general, overpressure or over-current phenomena can be certain.
Detection method: The focus of inspections should first eliminate excess pressure or short circuit, and then make other repairs.
Due to the different models, there are other factors that affect the normal startup. Then the following detection methods come in handy.
When the microprocessor (CPU), memory, program memory, and I/O integrated circuit operating power supply are all normal, they cannot be turned on. When further inspections are performed, the software should be used. First replace the user memory using substitution method (usually 24C16, 24C32, 24C64 and other models), if the fault still exists, under certain conditions, you can try to upgrade the FLASH program memory.
If you do not have the upgrade conditions, you can also use the oscilloscope to measure the transition of the SDA and SCL bus voltages of the memory at the instant of power-on to determine the fault location. In general, the main reasons for the non-booting are the normal operating conditions of the microprocessor (including the power supply, reset signal, crystal oscillation signal, memory communication signal, SDA/SCL signal, FLASH program memory communication signal), and user memory. Working conditions, working conditions of FLASH memory.
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