Skyworth is the oldest brother in television production. Although it is a big brother, it is also inevitable that it will happen. Many times we know that there is this failure, but we do not know why it occurred and how to solve it. We are all helpless. Don't worry, today Xiao Bian has compiled several common faults for Skyworth LCD TVs and its maintenance solutions. 
Symptoms: The sound is normal and there is no black screen.
Failure reason and overhaul:
First, turn on the power to turn on the TV, the sound is normal, and the LCD backlight is not bright. Use a multimeter to measure the 24V voltage that the power board supplies to the LED constant current driver board.
Second, check the motherboard backlight control signal output voltage, the voltage measured on the road is 4.6V normal. The fault is estimated on the LED constant current driver board. Because the LED constant current driver board is mainly composed of a CPU control circuit, a low voltage power supply system, an LED constant current driver and a DC/DC boost circuit. During normal operation, D4 on the LED constant current driver board will be bright (because D4 is the working indicator of the CPU on the LED constant current driver board). Check the LED constant current driver board 24V input fuse is not blown, measured CPU power supply 3.3V normal. According to maintenance experience, the basic role of the crystal oscillator in the circuit is to generate the clock frequency. After the crystal oscillator is broken, the entire digital circuit will not work. After replacing the 18M crystal oscillator on the CPU, the fault is eliminated.
Failure phenomenon: crash.
Failure reason and overhaul:
Plug in the power indicator light is not bright, test the motherboard has +5 V voltage output, check the CPU circuit, test CPU-KS88C4504 12th foot, 5th foot, 53rd foot power supply are normal, test CPU crystal Y2-10M has also been Vibration, post-test reset leg pin 19 voltage, normal should be high, and at this time is 0V, check the reset circuit and its periphery, the reset circuit is generated by an IC (Q3-DS1813), check Q3-DS1813 The power supply is normal, but the reset output is 0V. It is normal after replacing the Q3-DS1813.
Symptom: Can boot, but sometimes the boot is a white screen, after normal change, "Pleasewait character changes to the upper left corner of the screen when the power is turned on.
Failure reason and overhaul:
Because the characters sometimes shift, the analysis should be part of the CPU, bus voltage measurement, SCL is 3. 5V, and SDA is only about 0. 6V, suspected bad plug IC, disconnected U202TDA7440 21st and 22th feet are still the same , When unplug the high-frequency head connection after the bus back to normal, try to replace a high-frequency head is still, after power-on test high frequency power supply found FB200 power supply to 12V, the normal should be 5V, when the removal of FB200 is 5V, Analysis to 12V can only be caused by U804 (APX1117-5V) regulator IC, U804 input 12V, after the regulator output 5V by C827, FB200 after the power supply to the high-frequency head, after replacing the U804 machine is normal.
Symptoms: black screen. Failure reason and overhaul:
After turning on the power, the backlight is already on, but there is no OSD when the power is turned on. Therefore, it should be determined that the main board has not given the display signal. Test board J27 interface power supply is normal, but no LVDS signal, to determine the motherboard does not give screen drive signal, test board U15-PW113 108 feet VS and 109 feet HS, 106 feet DCLK output, RPH, RPI, RPF ? PG, RPD, RPE47 ohms out R, G, B data output, which can be determined that the LVDS chip U20-DS90C385 is not working, measuring U20 1,9,26 pin +3. 3V power supply is normal, the first 32 feet The ON/OFF control pin is also high, and it is normal after replacing U20.
Symptoms: Automatic shutdown from time to time.
Failure reason and overhaul:
When the power is turned off automatically, no power output is found and 300V is normal. 300V voltage is not drained after shutdown. It is considered that the fault should be in the primary of the power supply, and no obvious abnormality has been detected in each component. Upon inspection, it was found that when the accelerating voltage was increased, it was quickly shut down. Therefore, it is suspected that the ABL road will fail. . Check the ABL circuit components are normal, using replacement method one by one to replace, did not rule out the failure. In accordance with the routine inspection and replacement of R622 (0.22) resistance is also invalid that the fault should be in the power supply primary, after checking the primary power supply did not find an abnormality, try replacing R613 (0.18) troubleshooting!
Symptom: After turning on the blue screen for 2 seconds, the screen turns black. Failure reason and overhaul:
First of all, the voltage of each circuit is normal, and it is suspected that the main chip is working abnormally. If the external crystal is replaced, the fault still remains. The main chip was found to be abnormal and replaced. Abnormal DDR will also cause the main chip to work abnormally. Replace u14 (HY5DV56) DDR and the machine will return to normal.
Symptoms: Image disturbances.
Failure reason and overhaul:
Press the "menu" button after boot, and found that there is a very fine horizontal bar interference, careful observation of snow state, found that there are full screen moire interference, initialization is invalid, try to replace the image sound is still invalid. Switching to the AV state, the menu moire disappears. After the Av signal is connected, the interference appears. Try the HD channel. The fault phenomenon is the same as in the AV state. The MST6M19 or dynamic memory is suspected to be damaged, and the fault persists after the change. Is it caused by the driver board? Replacement troubleshooting. This driver board causes more malfunctions, such as normal green image menus.
Symptom: Cannot receive the station.
Failure reason and overhaul:
The inspection found that the image of snow was normal. There was no image flashing when the station was searched. The 5V and 33V power supply was normal. It was suspected that there was a problem with the AGC. The inspection found that the AGC voltage was 0.6V, which was low. After checking along the line, it was found that the C400 was leaking and was normal after replacement.
Symptoms: The red light does not turn on.
Failure reason and overhaul:
The power-on 5V is normal, 12V and 24V have no output, and the motherboard STBY feedback signal has no voltage, indicating that the motherboard is abnormal. Forced boot, each voltage is normal, but the fault persists, judged as data corruption or CPU not working. First of all, check the CPU operating voltage, crystal, bus, etc. are normal, re-write FLASH no results. Check the communication between the FLASH and the CPU bus and find that the R252 is open circuit and returns to normal after the replacement.
Symptoms: Cold boot black screen, shut down and then normal. Failure reason and overhaul:
This fault is generally caused by poor component performance. After replacing the ZM03 crystal, when the fault occurs, the hand crystal can be normal. Since the ZM03 has been replaced, replace the resonant capacitor CMl33 and CMl34 next to the crystal and troubleshoot the fault.
Symptoms: The sound is normal and there is no black screen.
Failure reason and overhaul:
First, turn on the power to turn on the TV, the sound is normal, and the LCD backlight is not bright. Use a multimeter to measure the 24V voltage that the power board supplies to the LED constant current driver board.
Second, check the motherboard backlight control signal output voltage, the voltage measured on the road is 4.6V normal. The fault is estimated on the LED constant current driver board. Because the LED constant current driver board is mainly composed of a CPU control circuit, a low voltage power supply system, an LED constant current driver and a DC/DC boost circuit. During normal operation, D4 on the LED constant current driver board will be bright (because D4 is the working indicator of the CPU on the LED constant current driver board). Check the LED constant current driver board 24V input fuse is not blown, measured CPU power supply 3.3V normal. According to maintenance experience, the basic role of the crystal oscillator in the circuit is to generate the clock frequency. After the crystal oscillator is broken, the entire digital circuit will not work. After replacing the 18M crystal oscillator on the CPU, the fault is eliminated.
Failure phenomenon: crash.
Failure reason and overhaul:
Plug in the power indicator light is not bright, test the motherboard has +5 V voltage output, check the CPU circuit, test CPU-KS88C4504 12th foot, 5th foot, 53rd foot power supply are normal, test CPU crystal Y2-10M has also been Vibration, post-test reset leg pin 19 voltage, normal should be high, and at this time is 0V, check the reset circuit and its periphery, the reset circuit is generated by an IC (Q3-DS1813), check Q3-DS1813 The power supply is normal, but the reset output is 0V. It is normal after replacing the Q3-DS1813.
Symptom: Can boot, but sometimes the boot is a white screen, after normal change, "Pleasewait character changes to the upper left corner of the screen when the power is turned on.
Failure reason and overhaul:
Because the characters sometimes shift, the analysis should be part of the CPU, bus voltage measurement, SCL is 3. 5V, and SDA is only about 0. 6V, suspected bad plug IC, disconnected U202TDA7440 21st and 22th feet are still the same , When unplug the high-frequency head connection after the bus back to normal, try to replace a high-frequency head is still, after power-on test high frequency power supply found FB200 power supply to 12V, the normal should be 5V, when the removal of FB200 is 5V, Analysis to 12V can only be caused by U804 (APX1117-5V) regulator IC, U804 input 12V, after the regulator output 5V by C827, FB200 after the power supply to the high-frequency head, after replacing the U804 machine is normal.
Symptoms: black screen. Failure reason and overhaul:
After turning on the power, the backlight is already on, but there is no OSD when the power is turned on. Therefore, it should be determined that the main board has not given the display signal. Test board J27 interface power supply is normal, but no LVDS signal, to determine the motherboard does not give screen drive signal, test board U15-PW113 108 feet VS and 109 feet HS, 106 feet DCLK output, RPH, RPI, RPF ? PG, RPD, RPE47 ohms out R, G, B data output, which can be determined that the LVDS chip U20-DS90C385 is not working, measuring U20 1,9,26 pin +3. 3V power supply is normal, the first 32 feet The ON/OFF control pin is also high, and it is normal after replacing U20.
Symptoms: Automatic shutdown from time to time.
Failure reason and overhaul:
When the power is turned off automatically, no power output is found and 300V is normal. 300V voltage is not drained after shutdown. It is considered that the fault should be in the primary of the power supply, and no obvious abnormality has been detected in each component. Upon inspection, it was found that when the accelerating voltage was increased, it was quickly shut down. Therefore, it is suspected that the ABL road will fail. . Check the ABL circuit components are normal, using replacement method one by one to replace, did not rule out the failure. In accordance with the routine inspection and replacement of R622 (0.22) resistance is also invalid that the fault should be in the power supply primary, after checking the primary power supply did not find an abnormality, try replacing R613 (0.18) troubleshooting!
Symptom: After turning on the blue screen for 2 seconds, the screen turns black. Failure reason and overhaul:
First of all, the voltage of each circuit is normal, and it is suspected that the main chip is working abnormally. If the external crystal is replaced, the fault still remains. The main chip was found to be abnormal and replaced. Abnormal DDR will also cause the main chip to work abnormally. Replace u14 (HY5DV56) DDR and the machine will return to normal.
Symptoms: Image disturbances.
Failure reason and overhaul:
Press the "menu" button after boot, and found that there is a very fine horizontal bar interference, careful observation of snow state, found that there are full screen moire interference, initialization is invalid, try to replace the image sound is still invalid. Switching to the AV state, the menu moire disappears. After the Av signal is connected, the interference appears. Try the HD channel. The fault phenomenon is the same as in the AV state. The MST6M19 or dynamic memory is suspected to be damaged, and the fault persists after the change. Is it caused by the driver board? Replacement troubleshooting. This driver board causes more malfunctions, such as normal green image menus.
Symptom: Cannot receive the station.
Failure reason and overhaul:
The inspection found that the image of snow was normal. There was no image flashing when the station was searched. The 5V and 33V power supply was normal. It was suspected that there was a problem with the AGC. The inspection found that the AGC voltage was 0.6V, which was low. After checking along the line, it was found that the C400 was leaking and was normal after replacement.
Symptoms: The red light does not turn on.
Failure reason and overhaul:
The power-on 5V is normal, 12V and 24V have no output, and the motherboard STBY feedback signal has no voltage, indicating that the motherboard is abnormal. Forced boot, each voltage is normal, but the fault persists, judged as data corruption or CPU not working. First of all, check the CPU operating voltage, crystal, bus, etc. are normal, re-write FLASH no results. Check the communication between the FLASH and the CPU bus and find that the R252 is open circuit and returns to normal after the replacement.
Symptoms: Cold boot black screen, shut down and then normal. Failure reason and overhaul:
This fault is generally caused by poor component performance. After replacing the ZM03 crystal, when the fault occurs, the hand crystal can be normal. Since the ZM03 has been replaced, replace the resonant capacitor CMl33 and CMl34 next to the crystal and troubleshoot the fault.