Many users are at home in LG, but LG often fails. When this happens, many users do not know what to do. Today Xiao Bian has listed several common faults in LG LCD TVs and analyzed the reasons with the majority of users.
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1, the entire monitor without electricity
(1) Power failure:
This is a fault that should be said to be a very simple one. The general LCD monitors have both internal and external power supplies. Regardless of the kind of power supply, its structure is much simpler than the power supply of the crt display. The fragile components are generally small components such as fuses and rectifier bridges. The power board is commonly used ic:6841 203d06, these commonly used pmw chips can be purchased in my professional LCD accessories shop.
(2) Driver board failure:
Drive board burn insurance or regulator chip failure, some of the machine is to switch power supply built-in, output two sets of power, one set is 5V for signal processing, the other set is 12V to provide high voltage board point backlight, if Some failures in the circuit of the switching power supply may result in no output of both sets of power supplies. First check the 12V voltage is normal, follow the check 5V voltage is normal, because the A/D driver board MCU chip operating voltage is 5V, so when the fault can not be found when the machine can not be measured, use a multimeter to measure 5V voltage, if there is no 5V voltage or The 5V voltage becomes very low, then one kind may be a problem with the input stage of the power circuit, that is to say that the 12V to 5V power supply part has a problem, this kind of fault is very common, check the 5 terminal regulator block (common type 8050SD -LM2596-AIC15-01, etc.)
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Another possibility is that the 5V load is getting heavier. The 5V voltage is pulled very low. In other words, the signal processing circuit at the rear stage has a problem, some of the circuits are damaged, and the load is aggravated, pulling the 5V voltage. Very low, one by one after the investigation of the problem of the components after the problem, replace the failed components, 5V can return to normal, the fault is generally resolved, but also often encountered after 5V voltage returned to normal can not normally boot, this situation is also more One reason is that on the one hand, the MCU's program is washed away, which may cause no boot, and the MCU itself is damaged. For example, the I/O port of the MCU is damaged, so that the MCU cannot scan the keys, and this type of failure caused by the MCU is encountered. The problem of finding the hardware is useless, even if you change the MCU can not solve the problem, because the MCU is the need to program and write code, in the case of no way to find the original AD driver board replacement, we can only use the general A/D driver board substitution such as: 151D or 161B
2, the display light will not shine, but the power indicator light is always on
This kind of problem is generally caused by high voltage anomalies, and it is the protection circuit action. In this case, the LCD screen is generally displayed. The method of viewing is “strabismusâ€.
3, black screen, no backlight, power light green light
Strabismus LCD display images, mostly high voltage board power supply circuit problems. Focus on checking whether the 12V power supply (Fuse F) and 3V or 5V switch voltage are normal. If there is no output switch control voltage because of MCU problems, the 3-terminal regulator block (AIC1084) 3.3V can be directly used instead. Ideas for Repairing High-Voltage Boards (Power Fuse - Switch Control Tube - Power Management IC - Push-Pull Big Pipe - Power Switch Tube - DA Conversion Circuit (Energy Storage Inductor, Rectifier) ​​- LC Boost Circuit (Step-Up Transformer, Boost Capacitor) - Coupling Capacitor - Lamp.
4, the screen bright line, bright band or dark line
This problem is generally a fault of the LCD screen. The bright line fault is usually caused by the problem of the line connecting the LCD panel body or the damage of the driver IC of a row and column.
The dark line is generally the body of the screen has leakage, or TAB flexible board connection open circuit. The above two problems are basically the death penalty for the machine, there is no maintenance value, because the price of a screen is too high.
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5, color cast failure
Generally can enter the factory adjustment mode to adjust. Without this model, maintenance ideas: replace the screen line and adapter plate - rewrite the driver - driver board is bad (uncommon) - the screen backplane control IC is bad (uncommon) - unplug the screen to observe the backlight color (backlight Flat color for lamp aging) - Lamp replacement
6, character virtual or trailing
Check the VGA signal line, focus on whether the RGB tricolor line ground connection is normal - replace the screen line or adapter plate - rewrite the driver - change the driver board - LCD screen backplane signal interface IC bad - LCD screen backplane contrast potential Adjuster - LCD screen light guide plate misalignment - polarizer misalignment
7. There are stains on the LCD screen to wipe or replace the protective film - open the screen to clean the outer polarizer and plexiglass (with cotton balls, purified water treatment) - hairdryer drying
8, LCD screen highlights
One or two large bright spots, you can try to lightly press the bright spot with your fingertips, can disappear, indicating that the switch and the electrode for this pixel is virtually connected. The small black spots and gray spots may be caused by dust on the internal light guide plate or polarizer, and can be cleaned.
9, LCD screen brightness is low
Check ADJ brightness adjustment circuit of high voltage board - Lamp replacement - Replacement high voltage board - Adjust or replace the light guide plate
10, error "out of frequency range"
Check Signal Line - Rewrite MCU Driver - Replace EPROM - Rewrite EPROM Program - Change Drive Board
11, after power on without pressing the switch button that is a white screen backlight, the key can be displayed normally
High-voltage board interface switch signal and ADJ signal reverse connection caused, part of the driver board MCU switch signal output is not normal, you can rewrite MCU program repair - change MCU![]()
Switching power supply failure:
1. Fused wire blown
For the fuse fuse failure, usually the main power supply rectifier filter circuit filter capacitor, rectifier diodes and other components. Of course, when the anti-interference circuit fails, it also causes the fuse to blow and black. It must be noted that the blowing of the fuse caused by the breakdown of the switch is usually accompanied by the simultaneous damage of the overcurrent detection resistor and the power control integrated circuit. Negative temperature coefficient thermistors are also easier to burn together with the fuses, and inspections should also be performed during inspections.
2. No voltage output, but the fuse is not blown
There was no voltage output, but the fuse was not blown, indicating that the switching power supply circuit did not work or entered protection after work. When overhauling, first measure whether the starting pin of the power control integrated circuit start-up pin has a starting voltage.
(1) If there is no starting voltage or the starting voltage is too low, check whether there is a leakage phenomenon between the starting resistor and the external components of the pin.
(2) If there is a starting voltage, then measure whether the output terminal of the power control integrated circuit has a high and low jumping level signal at the moment of starting.
• If there is no transition, it means that the power supply control IC itself or its peripheral oscillator circuit components or protection circuit is faulty. You can use the substitute power supply to control the IC and check the external components to find the fault. If there is a jump, most of the switches themselves are bad or damaged, and they should be checked.
3. The output voltage is too low
The cause of the output voltage of the switching power supply output is too low. In addition to the abnormality in the voltage regulator control circuit, there are usually three reasons:
(1) The performance of the switch decreases. This situation can cause the switch tube to fail to conduct normally, which increases the internal resistance of the power supply and deteriorates the ability to carry the load.
(2) Output rectifier diodes and filter capacitors fail. This situation can be judged by substitution methods to see if they are damaged.
(3) The load of the switching power supply has a short-circuit fault. In particular, the DC/DC converter is short-circuited or has poor performance. In this regard, the method of disconnecting the entire load of the switching power supply circuit may be used to distinguish whether the switching power supply circuit is defective or the load circuit is faulty. When the load circuit is disconnected, the voltage at the output terminal returns to normal, which means that the load is too heavy. If it is still unable to return to normal, the switching power supply circuit is faulty.
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4. The output voltage is too high
The output voltage is too high. Most of the faults occur in the switching power supply's regulator sampling and regulation control circuit. The components in the feedback loop consisting of sampling resistors, error sampling amplifiers, optocouplers, power supply control integrated circuits, etc. should be inspected. In general, the incidence of damage to the sampling resistor, precision voltage regulator amplifier, or optocoupler is high.
For the over-voltage phenomenon of the switching power supply with an over-voltage protection circuit, the over-voltage protection circuit may be disconnected first, and then the voltage at the main output of the power supply may be quickly measured at the moment of starting. If the measured voltage is still higher than the normal value (generally higher than 1V, it is a high voltage fault), it should be overhauled according to the above high voltage fault.
Suggest:
For the aging of the lamp replacement screen to find out the size of the lamp, because despite the same screen size, but the lamp length and thickness slightly different, if you can not find the same size lamp, if you can use a short lamp is good If not, use a longer knife with a scalpel to carefully remove the screen frame and insulate it with a heat-shrink tube.
Tags: Smart TV Communication, Smart TV Forum
1, the entire monitor without electricity
(1) Power failure:
This is a fault that should be said to be a very simple one. The general LCD monitors have both internal and external power supplies. Regardless of the kind of power supply, its structure is much simpler than the power supply of the crt display. The fragile components are generally small components such as fuses and rectifier bridges. The power board is commonly used ic:6841 203d06, these commonly used pmw chips can be purchased in my professional LCD accessories shop.
(2) Driver board failure:
Drive board burn insurance or regulator chip failure, some of the machine is to switch power supply built-in, output two sets of power, one set is 5V for signal processing, the other set is 12V to provide high voltage board point backlight, if Some failures in the circuit of the switching power supply may result in no output of both sets of power supplies. First check the 12V voltage is normal, follow the check 5V voltage is normal, because the A/D driver board MCU chip operating voltage is 5V, so when the fault can not be found when the machine can not be measured, use a multimeter to measure 5V voltage, if there is no 5V voltage or The 5V voltage becomes very low, then one kind may be a problem with the input stage of the power circuit, that is to say that the 12V to 5V power supply part has a problem, this kind of fault is very common, check the 5 terminal regulator block (common type 8050SD -LM2596-AIC15-01, etc.)
Another possibility is that the 5V load is getting heavier. The 5V voltage is pulled very low. In other words, the signal processing circuit at the rear stage has a problem, some of the circuits are damaged, and the load is aggravated, pulling the 5V voltage. Very low, one by one after the investigation of the problem of the components after the problem, replace the failed components, 5V can return to normal, the fault is generally resolved, but also often encountered after 5V voltage returned to normal can not normally boot, this situation is also more One reason is that on the one hand, the MCU's program is washed away, which may cause no boot, and the MCU itself is damaged. For example, the I/O port of the MCU is damaged, so that the MCU cannot scan the keys, and this type of failure caused by the MCU is encountered. The problem of finding the hardware is useless, even if you change the MCU can not solve the problem, because the MCU is the need to program and write code, in the case of no way to find the original AD driver board replacement, we can only use the general A/D driver board substitution such as: 151D or 161B
2, the display light will not shine, but the power indicator light is always on
This kind of problem is generally caused by high voltage anomalies, and it is the protection circuit action. In this case, the LCD screen is generally displayed. The method of viewing is “strabismusâ€.
3, black screen, no backlight, power light green light
Strabismus LCD display images, mostly high voltage board power supply circuit problems. Focus on checking whether the 12V power supply (Fuse F) and 3V or 5V switch voltage are normal. If there is no output switch control voltage because of MCU problems, the 3-terminal regulator block (AIC1084) 3.3V can be directly used instead. Ideas for Repairing High-Voltage Boards (Power Fuse - Switch Control Tube - Power Management IC - Push-Pull Big Pipe - Power Switch Tube - DA Conversion Circuit (Energy Storage Inductor, Rectifier) ​​- LC Boost Circuit (Step-Up Transformer, Boost Capacitor) - Coupling Capacitor - Lamp.
4, the screen bright line, bright band or dark line
This problem is generally a fault of the LCD screen. The bright line fault is usually caused by the problem of the line connecting the LCD panel body or the damage of the driver IC of a row and column.
The dark line is generally the body of the screen has leakage, or TAB flexible board connection open circuit. The above two problems are basically the death penalty for the machine, there is no maintenance value, because the price of a screen is too high.
5, color cast failure
Generally can enter the factory adjustment mode to adjust. Without this model, maintenance ideas: replace the screen line and adapter plate - rewrite the driver - driver board is bad (uncommon) - the screen backplane control IC is bad (uncommon) - unplug the screen to observe the backlight color (backlight Flat color for lamp aging) - Lamp replacement
6, character virtual or trailing
Check the VGA signal line, focus on whether the RGB tricolor line ground connection is normal - replace the screen line or adapter plate - rewrite the driver - change the driver board - LCD screen backplane signal interface IC bad - LCD screen backplane contrast potential Adjuster - LCD screen light guide plate misalignment - polarizer misalignment
7. There are stains on the LCD screen to wipe or replace the protective film - open the screen to clean the outer polarizer and plexiglass (with cotton balls, purified water treatment) - hairdryer drying
8, LCD screen highlights
One or two large bright spots, you can try to lightly press the bright spot with your fingertips, can disappear, indicating that the switch and the electrode for this pixel is virtually connected. The small black spots and gray spots may be caused by dust on the internal light guide plate or polarizer, and can be cleaned.
9, LCD screen brightness is low
Check ADJ brightness adjustment circuit of high voltage board - Lamp replacement - Replacement high voltage board - Adjust or replace the light guide plate
10, error "out of frequency range"
Check Signal Line - Rewrite MCU Driver - Replace EPROM - Rewrite EPROM Program - Change Drive Board
11, after power on without pressing the switch button that is a white screen backlight, the key can be displayed normally
High-voltage board interface switch signal and ADJ signal reverse connection caused, part of the driver board MCU switch signal output is not normal, you can rewrite MCU program repair - change MCU
Switching power supply failure:
1. Fused wire blown
For the fuse fuse failure, usually the main power supply rectifier filter circuit filter capacitor, rectifier diodes and other components. Of course, when the anti-interference circuit fails, it also causes the fuse to blow and black. It must be noted that the blowing of the fuse caused by the breakdown of the switch is usually accompanied by the simultaneous damage of the overcurrent detection resistor and the power control integrated circuit. Negative temperature coefficient thermistors are also easier to burn together with the fuses, and inspections should also be performed during inspections.
2. No voltage output, but the fuse is not blown
There was no voltage output, but the fuse was not blown, indicating that the switching power supply circuit did not work or entered protection after work. When overhauling, first measure whether the starting pin of the power control integrated circuit start-up pin has a starting voltage.
(1) If there is no starting voltage or the starting voltage is too low, check whether there is a leakage phenomenon between the starting resistor and the external components of the pin.
(2) If there is a starting voltage, then measure whether the output terminal of the power control integrated circuit has a high and low jumping level signal at the moment of starting.
• If there is no transition, it means that the power supply control IC itself or its peripheral oscillator circuit components or protection circuit is faulty. You can use the substitute power supply to control the IC and check the external components to find the fault. If there is a jump, most of the switches themselves are bad or damaged, and they should be checked.
3. The output voltage is too low
The cause of the output voltage of the switching power supply output is too low. In addition to the abnormality in the voltage regulator control circuit, there are usually three reasons:
(1) The performance of the switch decreases. This situation can cause the switch tube to fail to conduct normally, which increases the internal resistance of the power supply and deteriorates the ability to carry the load.
(2) Output rectifier diodes and filter capacitors fail. This situation can be judged by substitution methods to see if they are damaged.
(3) The load of the switching power supply has a short-circuit fault. In particular, the DC/DC converter is short-circuited or has poor performance. In this regard, the method of disconnecting the entire load of the switching power supply circuit may be used to distinguish whether the switching power supply circuit is defective or the load circuit is faulty. When the load circuit is disconnected, the voltage at the output terminal returns to normal, which means that the load is too heavy. If it is still unable to return to normal, the switching power supply circuit is faulty.
4. The output voltage is too high
The output voltage is too high. Most of the faults occur in the switching power supply's regulator sampling and regulation control circuit. The components in the feedback loop consisting of sampling resistors, error sampling amplifiers, optocouplers, power supply control integrated circuits, etc. should be inspected. In general, the incidence of damage to the sampling resistor, precision voltage regulator amplifier, or optocoupler is high.
For the over-voltage phenomenon of the switching power supply with an over-voltage protection circuit, the over-voltage protection circuit may be disconnected first, and then the voltage at the main output of the power supply may be quickly measured at the moment of starting. If the measured voltage is still higher than the normal value (generally higher than 1V, it is a high voltage fault), it should be overhauled according to the above high voltage fault.
Suggest:
For the aging of the lamp replacement screen to find out the size of the lamp, because despite the same screen size, but the lamp length and thickness slightly different, if you can not find the same size lamp, if you can use a short lamp is good If not, use a longer knife with a scalpel to carefully remove the screen frame and insulate it with a heat-shrink tube.
Tags: Smart TV Communication, Smart TV Forum
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