When the television is used for a long time, there will be a variety of failures, and many users have expressed their insecurities to find repair personnel intelligently to repair, but sometimes users will spend a lot of money. Today, Xiao Bian put together a list of common faults and maintenance plans for Changhong TV. Everyone hastened to collect them in case of emergency.
Common malfunctions
1, black screen (power indicator light)
1) Check whether the inverter works, such as the lamp is not lit, first check the control signal STANDBY is normal, and then check the inverter power supply +12 V, 5 V is normal, no power supply is normally +12 V fuse resistor open circuit, replace it, If the power supply is normal and the lamp is still off, you need to replace the inverter board.
2) Under the premise that the lamp is on, it is necessary to check whether the LCD power supply VCCPANEL (3.3V) is normal. If it is abnormal, check the LCD power control signal BLON (normal should be high), if not, you need to Check whether the CPU is working properly. Normally, the CPU needs to be replaced. If the control signal is normal and there is no 3.3V power supply, you need to replace SI9430DY (U15).
2, white screen (the entire screen shows a very bright white grating)
1) First, check whether the connection lines (PJ1, PJ2) between the LCD panel and the signal board are in poor contact. If the connection is bad, reconnect the connector.
2) Another common situation is that the A/D converter power supply PVDD (3.3V) drops even to 0V, the AD9884 (U4) does not work, there is no digital RGB signal output, and the liquid crystal screen signal electrode has no operating voltage, equivalent to the liquid crystal cell Without power, the principle of the display shows that: the liquid crystal screen is in a transparent state, so the entire screen shows a bright white grating. After inspection, the L11 inductor fails early and the resistance value increases, causing the PVDD power supply to drop.
3, screen color cast
If there is a slight color cast on the screen, first enter the factory mode (turn the monitor off by turning the power switch, then hold down the “ †key and the “SELECT†key, and then turn on the power switch). At this time, enter the swipe screen and notice that the screen appears Asymmetric interference fringes, at this time need to check 24C16 (U9), even if the measurement of the working voltage is normal, must also be replaced, under normal circumstances can be replaced to repair.
4, screen color
In this case, the A/D converter has no analog R or G or B signal input, and it is checked that L3 or L4 or L5 fails early, and the resistance value increases or opens, resulting in no primary color signal input.
5, red screen
If a red screen appears on the entire screen, check the frame memories U2 and U3. Even if the memory power is normal, you must consider replacing them. Under normal circumstances, you need to replace U2.
6, there is "signal out of range"
In this case, the monitor should first exclude signals that are not standard or exceed the display. Supported Display Formats In these two cases, such as a display failure, the analog line and field synchronization signals must be checked. In general, early failure of R39 and R40 results in an increase in resistance or an open circuit, resulting in no line field synchronization signal. Input A/D converter.
Changhong TV common fault judgment
1. The Changhong C2188 TV raster is a known horizontal bright line and burns the pump power circuit V36 to breakdown.
2, Changhong C2188 TV a horizontal bright line field scanning circuit TA7698 (29) foot voltage abnormality, 306 leakage.
3, Changhong C2188 TV lights up after power, non-raster power circuit +B (115V) is about 80V, VQ822 breakdown.
4. After the Changhong C2188 TV is turned on, it is muted, the switching transformer emits a humming switch power supply circuit +B (115V) with a voltage of 87V, and the NQ826 breaks down.
5, Changhong C2169 TV no color, black and white images and audio normal color channel circuit N201 (12) foot voltage is 6V, normal 9V, R916 open circuit.
6. After the Changhong C2589 TV is turned on, the grating suffers serious pincushion distortion. The pincushion correction circuit 27V is out of order, and the VQ45 output voltage is -15.6V. The C474 (10F/160V) is open circuit.
7. The Changhong C2589 TV has black and white images and audio, and the colorless color subcarrier recovery circuit TA8628 (18) has a foot voltage of 4V and C518 leakage.
Common Faults and Maintenance of Changhong TV Common Types
1, Changhong TV LT32876 sometimes does not boot, sometimes automatically shut down after boot
Analysis and Maintenance: It was found that the power indicator was bright yellow after the power was turned on, and that it could not be turned on again at this time. Normally, the power indicator should be red during standby. According to the user's response, even after the red light is turned on normally, the power indicator will turn yellow and turn off automatically after a few minutes.
Suspected that the crystal or reset circuit is working abnormally. When checking the reset transistor Q21, the voltage of the C electrode is found to be about 2V. After the normal reset is completed, the voltage should be 0V. Then the external capacitor C304 of Q21B is no longer available. The machine is normal.
2, Changhong TV L6599D can not boot
Analysis and Maintenance: After starting up, the power-on control voltage is +4.6V, and Q14 is saturated. The starting voltage of IC1 (12) is +9V (normal is +13.5V to 15V). It is doubtful that Q11 is bad. After the short-circuiting of the emitter and collector of Q11, there is still only 9V. This indicates that the fault was discharged in the circuit connected to the starting voltage and replaced by U1, indicating that the fault was caused by a short circuit in the internal circuit.
3, Changhong TV FSP242 three no
Analysis and Maintenance: The measurement is started, the fuse is good, and the measured voltage of C2 is about 295V across the mains rectified and filtered. C1 has 308V at both ends, but the measured auxiliary power has no 5V output, and the fault is determined in the auxiliary power circuit. Measure the voltage of the (8) pin of the sub power supply driver circuit TEA1532. Check the start circuit of the (8) pin and find that the current limiting resistor R is blown.
However, the current-limiting resistor R of the start-up circuit is replaced and then blown again, which indicates that the sub-supply circuit TEA1532 circuit has a serious short-circuit fault, disconnects the external circuit of the foot (8), measures the resistance of the foot (8) to ground, and judges the internal circuit of the TEA1532 is damaged. . After replacing the TEA1532 and the current limiting resistor R, troubleshoot.
4, Changhong TV LT32600 power test machine, LCD TV yellow indicator light, remote control does not work
Analysis and maintenance: The power of each foot of U13 (FLASH) was detected. It was found that except for foot (4), the rest of the foot voltage was 3.3V. It is initially determined that U9 (MST9U88L-LF) has not entered the working state. Detection of the CPU's power supply are normal, using the oscilloscope to measure the crystal oscillation waveform, STANDBY signal U9 (190) pin is 2.82V normal, (253) pin SYSRST low-level normal, (93) pin PWM3-PANEL voltage is Abnormality of 0.67V (normally 2.2V). After searching, it was found that the pull-up resistor R66 (lkΩ) was open and the TV returned to normal after replacing the R66.
5, CHANGHONG TV LT26810U indicator light does not turn on
Analysis and Maintenance: Based on the fault phenomenon, the initial determination of the fault control system circuit in the signal processing board. The aircraft's control system circuit is mainly composed of user memory U14 (24C32), FLASHU19 (M25P64) and the main chip U34 (MT8222) internal part of the module circuit. Control system circuit to work, first of all its power supply voltage must be normal, the machine signal processing circuit in the user memory, the main chip, FLASH required operating voltage by the DC-DC circuit U3, Ull, U7, U8 provided.
Check the output voltage of the DC-DC circuit and find that the DC-DC circuit U7 has no 3.3V voltage output. The relevant circuit is shown in the figure below. Measure the resistance of the U(4) pin to ground. No component breakdown short circuit condition was found. Check the components in the U7 external circuit, found that Q9 is open, and troubleshooting after replacing Q9.
Common malfunctions
1, black screen (power indicator light)
1) Check whether the inverter works, such as the lamp is not lit, first check the control signal STANDBY is normal, and then check the inverter power supply +12 V, 5 V is normal, no power supply is normally +12 V fuse resistor open circuit, replace it, If the power supply is normal and the lamp is still off, you need to replace the inverter board.
2) Under the premise that the lamp is on, it is necessary to check whether the LCD power supply VCCPANEL (3.3V) is normal. If it is abnormal, check the LCD power control signal BLON (normal should be high), if not, you need to Check whether the CPU is working properly. Normally, the CPU needs to be replaced. If the control signal is normal and there is no 3.3V power supply, you need to replace SI9430DY (U15).
2, white screen (the entire screen shows a very bright white grating)
1) First, check whether the connection lines (PJ1, PJ2) between the LCD panel and the signal board are in poor contact. If the connection is bad, reconnect the connector.
2) Another common situation is that the A/D converter power supply PVDD (3.3V) drops even to 0V, the AD9884 (U4) does not work, there is no digital RGB signal output, and the liquid crystal screen signal electrode has no operating voltage, equivalent to the liquid crystal cell Without power, the principle of the display shows that: the liquid crystal screen is in a transparent state, so the entire screen shows a bright white grating. After inspection, the L11 inductor fails early and the resistance value increases, causing the PVDD power supply to drop.
3, screen color cast
If there is a slight color cast on the screen, first enter the factory mode (turn the monitor off by turning the power switch, then hold down the “ †key and the “SELECT†key, and then turn on the power switch). At this time, enter the swipe screen and notice that the screen appears Asymmetric interference fringes, at this time need to check 24C16 (U9), even if the measurement of the working voltage is normal, must also be replaced, under normal circumstances can be replaced to repair.
4, screen color
In this case, the A/D converter has no analog R or G or B signal input, and it is checked that L3 or L4 or L5 fails early, and the resistance value increases or opens, resulting in no primary color signal input.
5, red screen
If a red screen appears on the entire screen, check the frame memories U2 and U3. Even if the memory power is normal, you must consider replacing them. Under normal circumstances, you need to replace U2.
6, there is "signal out of range"
In this case, the monitor should first exclude signals that are not standard or exceed the display. Supported Display Formats In these two cases, such as a display failure, the analog line and field synchronization signals must be checked. In general, early failure of R39 and R40 results in an increase in resistance or an open circuit, resulting in no line field synchronization signal. Input A/D converter.
Changhong TV common fault judgment
1. The Changhong C2188 TV raster is a known horizontal bright line and burns the pump power circuit V36 to breakdown.
2, Changhong C2188 TV a horizontal bright line field scanning circuit TA7698 (29) foot voltage abnormality, 306 leakage.
3, Changhong C2188 TV lights up after power, non-raster power circuit +B (115V) is about 80V, VQ822 breakdown.
4. After the Changhong C2188 TV is turned on, it is muted, the switching transformer emits a humming switch power supply circuit +B (115V) with a voltage of 87V, and the NQ826 breaks down.
5, Changhong C2169 TV no color, black and white images and audio normal color channel circuit N201 (12) foot voltage is 6V, normal 9V, R916 open circuit.
6. After the Changhong C2589 TV is turned on, the grating suffers serious pincushion distortion. The pincushion correction circuit 27V is out of order, and the VQ45 output voltage is -15.6V. The C474 (10F/160V) is open circuit.
7. The Changhong C2589 TV has black and white images and audio, and the colorless color subcarrier recovery circuit TA8628 (18) has a foot voltage of 4V and C518 leakage.
Common Faults and Maintenance of Changhong TV Common Types
1, Changhong TV LT32876 sometimes does not boot, sometimes automatically shut down after boot
Analysis and Maintenance: It was found that the power indicator was bright yellow after the power was turned on, and that it could not be turned on again at this time. Normally, the power indicator should be red during standby. According to the user's response, even after the red light is turned on normally, the power indicator will turn yellow and turn off automatically after a few minutes.
Suspected that the crystal or reset circuit is working abnormally. When checking the reset transistor Q21, the voltage of the C electrode is found to be about 2V. After the normal reset is completed, the voltage should be 0V. Then the external capacitor C304 of Q21B is no longer available. The machine is normal.
2, Changhong TV L6599D can not boot
Analysis and Maintenance: After starting up, the power-on control voltage is +4.6V, and Q14 is saturated. The starting voltage of IC1 (12) is +9V (normal is +13.5V to 15V). It is doubtful that Q11 is bad. After the short-circuiting of the emitter and collector of Q11, there is still only 9V. This indicates that the fault was discharged in the circuit connected to the starting voltage and replaced by U1, indicating that the fault was caused by a short circuit in the internal circuit.
3, Changhong TV FSP242 three no
Analysis and Maintenance: The measurement is started, the fuse is good, and the measured voltage of C2 is about 295V across the mains rectified and filtered. C1 has 308V at both ends, but the measured auxiliary power has no 5V output, and the fault is determined in the auxiliary power circuit. Measure the voltage of the (8) pin of the sub power supply driver circuit TEA1532. Check the start circuit of the (8) pin and find that the current limiting resistor R is blown.
However, the current-limiting resistor R of the start-up circuit is replaced and then blown again, which indicates that the sub-supply circuit TEA1532 circuit has a serious short-circuit fault, disconnects the external circuit of the foot (8), measures the resistance of the foot (8) to ground, and judges the internal circuit of the TEA1532 is damaged. . After replacing the TEA1532 and the current limiting resistor R, troubleshoot.
4, Changhong TV LT32600 power test machine, LCD TV yellow indicator light, remote control does not work
Analysis and maintenance: The power of each foot of U13 (FLASH) was detected. It was found that except for foot (4), the rest of the foot voltage was 3.3V. It is initially determined that U9 (MST9U88L-LF) has not entered the working state. Detection of the CPU's power supply are normal, using the oscilloscope to measure the crystal oscillation waveform, STANDBY signal U9 (190) pin is 2.82V normal, (253) pin SYSRST low-level normal, (93) pin PWM3-PANEL voltage is Abnormality of 0.67V (normally 2.2V). After searching, it was found that the pull-up resistor R66 (lkΩ) was open and the TV returned to normal after replacing the R66.
5, CHANGHONG TV LT26810U indicator light does not turn on
Analysis and Maintenance: Based on the fault phenomenon, the initial determination of the fault control system circuit in the signal processing board. The aircraft's control system circuit is mainly composed of user memory U14 (24C32), FLASHU19 (M25P64) and the main chip U34 (MT8222) internal part of the module circuit. Control system circuit to work, first of all its power supply voltage must be normal, the machine signal processing circuit in the user memory, the main chip, FLASH required operating voltage by the DC-DC circuit U3, Ull, U7, U8 provided.
Check the output voltage of the DC-DC circuit and find that the DC-DC circuit U7 has no 3.3V voltage output. The relevant circuit is shown in the figure below. Measure the resistance of the U(4) pin to ground. No component breakdown short circuit condition was found. Check the components in the U7 external circuit, found that Q9 is open, and troubleshooting after replacing Q9.