Fault phenomenon:
After the power is turned on, the device is in the "three none" state, but the power indicator on the panel is normal.
The “three-nothing†state refers to the state where there is no image, sound, and grating after the TV is turned on.
Troubleshooting
The power indicator light is normal, indicating that the switching power supply is working normally.
Detection of switching power supply +B voltage is 129V normal, indicating that the switching power supply has been operating in a wide power pulse oscillation state, it is estimated that the fault is mostly caused by abnormal scanning circuit.
The main reasons that can cause the line scan circuit to work abnormally include: line oscillation circuit operating power supply voltage is too low or no voltage, row excitation circuit normal working conditions do not have or line excitation amplifier tube damage; line output circuit DC power supply line open circuit.
Therefore, to repair such faults, the output voltage of the output transistor V402 should be measured first. The actual measurement of the voltage is 130V.
Next, the 36-pin power supply input terminal N201 (TDA8362) of the oscillating circuit is tested to jump between 2.1V and 4.2V, which is obviously far from the normal value of 8.2V, indicating that the line oscillation circuit is not working. This voltage is the output of the power supply +24V true current through the resistor R845 step down, 8.2V regulator VD805 regulator, capacitor C480 filter formed, and by the standby control circuit V861, V862 as a state control.
This situation is mostly caused by problems with the 8.2V power supply. The V862 collector is welded open and the standby circuit is controlled by the 8.2V power supply circuit. The voltage across the C480 is still fluctuating between 2.1V and 4.2V. This eliminates the possibility of a failure of the standby control circuit component. Should focus on inspection of 8.2V power supply circuit components, the test found that the filter capacitor C480 serious leakage, replace the C480, restore the welding open V862 collector power test machine, the whole work to restore normal.
This content is copyrighted exclusively by SofaNet. Welcome manufacturers to further exchanges and cooperation with us to create more in-depth product reports.
Sofa Net is an Internet technology company specializing in smart TVs and boxes. It owns popular products such as sofa butlers, sofa tables, and sofa forums. It has been committed to providing high quality application resources for smart TV and TV box users and active community exchanges. And authoritative evaluation of smart TV products.
After the power is turned on, the device is in the "three none" state, but the power indicator on the panel is normal.
The “three-nothing†state refers to the state where there is no image, sound, and grating after the TV is turned on.
The power indicator light is normal, indicating that the switching power supply is working normally.
Detection of switching power supply +B voltage is 129V normal, indicating that the switching power supply has been operating in a wide power pulse oscillation state, it is estimated that the fault is mostly caused by abnormal scanning circuit.
The main reasons that can cause the line scan circuit to work abnormally include: line oscillation circuit operating power supply voltage is too low or no voltage, row excitation circuit normal working conditions do not have or line excitation amplifier tube damage; line output circuit DC power supply line open circuit.
Therefore, to repair such faults, the output voltage of the output transistor V402 should be measured first. The actual measurement of the voltage is 130V.
Next, the 36-pin power supply input terminal N201 (TDA8362) of the oscillating circuit is tested to jump between 2.1V and 4.2V, which is obviously far from the normal value of 8.2V, indicating that the line oscillation circuit is not working. This voltage is the output of the power supply +24V true current through the resistor R845 step down, 8.2V regulator VD805 regulator, capacitor C480 filter formed, and by the standby control circuit V861, V862 as a state control.
This situation is mostly caused by problems with the 8.2V power supply. The V862 collector is welded open and the standby circuit is controlled by the 8.2V power supply circuit. The voltage across the C480 is still fluctuating between 2.1V and 4.2V. This eliminates the possibility of a failure of the standby control circuit component. Should focus on inspection of 8.2V power supply circuit components, the test found that the filter capacitor C480 serious leakage, replace the C480, restore the welding open V862 collector power test machine, the whole work to restore normal.
This content is copyrighted exclusively by SofaNet. Welcome manufacturers to further exchanges and cooperation with us to create more in-depth product reports.
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Sofa Net is an Internet technology company specializing in smart TVs and boxes. It owns popular products such as sofa butlers, sofa tables, and sofa forums. It has been committed to providing high quality application resources for smart TV and TV box users and active community exchanges. And authoritative evaluation of smart TV products.
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