If there is flickering light on the edge of the TV, it should be caused by light leakage on the TV screen.In this case, it is better to call the official customer service for repair, and let the professional master come to repair the glue. However, if it is a problem with the motherboard, it should be repaired or replaced.Mainboard maintenance requires professional maintenance experience, solid theoretical foundation and special tools.If you don't have these conditions, it is recommended that you directly ask a professional after-sales technician for on-site maintenance. 1. The whole display has no power (1) Power failure: It should be said that this is a very simple failure. Generally, there are two types of power supply inside the LCD unit and outside the unit, and some are common outside the unit.No matter what kind of power supply, its structure is much simpler than the power supply of CRT display, and the vulnerable parts are generally some small components, such as fuse and rectifier bridge.Common IC of power panel: 6841203d06. These commonly used pmw chips can be bought in professional LCD accessory stores like mine.(2) Drive board failure: the drive board is burned out or the voltage regulator chip fails. Some machines have built-in switching power supplies and output two groups of power supplies, one of which is 5V for signal processing, and the other is 12V for high-voltage board point backlighting. If the circuit of the switching power supply fails, it may lead to no output of both groups of power supplies. Check whether the 12V voltage is normal first, and then check whether the 5V voltage is normal. Because the working voltage of the MCU chip of the A/D drive board is 5V, when finding the fault that the machine cannot be started, first use a multimeter to measure the 5V voltage. If there is no 5V voltage or the 5V voltage becomes very low, then one possibility is that there is a problem in the input stage of the power supply circuit, that is, there is a problem in the part of the 12V to 5V power supply,This kind of fault is very common. Check the 5-terminal voltage stabilizing block (common model 8050SD-LM2596-AIC15-01, etc.). Another possibility is that the 5V load is increased, and the 5V voltage is pulled very low. In other words, there is a problem in the signal processing circuit of the later stage, some circuits are damaged, causing the load to increase, and the 5V voltage is pulled very low. Check the faulty components of the later stage one by one. After replacing the faulty components, the 5V can return to normal, and the fault is generally solved,It is also common to encounter the failure to start up normally after the 5V voltage returns to normal. There are many reasons for this. On the one hand, the MCU program may not start up because it is flushed out, and on the other hand, the MCU itself is damaged. For example, the I/O port of the MCU is damaged, making the MCU unable to scan keys. In case of this kind of failure caused by the MCU, it is useless to find hardware problems,Even if you replace the MCU, it will not solve the problem, because the MCU needs to be programmed and coded. If we can't find the original AD driver board to replace it, we can only replace it with a general A/D driver board, such as 151D or 161B. 2. The display screen will not light up once it is lit, but the power indicator light is always green. This problem is generally caused by abnormal high voltage, which is the action of the protection circuit,In this case, there is a display on the LCD screen, and the way to see it is squint. 3. The display screen is black, without backlight, and the green light of the power light is always on. The squint LCD screen has a display image, which mostly belongs to the problem of high-voltage board power supply circuit.Check whether the 12V power supply (fuse F) and the switching voltage of 3V or 5V are normal.If there is no output switch control voltage due to MCU problems, you can directly extract (AIC1084) 3.3V from the 3-terminal voltage regulator block to replace it. The idea of repairing the high-voltage board (power fuse - switch control tube - power management IC - push-pull generator tube - power switch tube - DA conversion circuit (energy storage inductance, rectifier tube) - LC step-up circuit (step-up transformer, step-up capacitor) - coupling capacitor - lamp tube. 4. The problem of bright lines, bright bands or dark lines on the screen is generally caused by the failure of the LCD screen.The bright line fault is generally caused by the problem of the flat cable connecting to the LCD body or the damage of the drive IC of a row and column.The hidden line is generally caused by the leakage of the screen body, or the open circuit of the TAB flexible board wiring.The above two problems are basically the death penalty for the machine, which has no maintenance value, because the price of a screen is too high. 5. Color deviation fault can generally be adjusted by entering factory adjustment mode.If this mode is not available, the maintenance idea is: replace the screen cable and adapter board - rewrite the driver - the driver board is broken (uncommon) - the control IC of the screen backplane is broken (uncommon) - unplug the screen cable to observe the backlight color (flat backlight color means the lamp tube is aging) - replace the lamp tube. 6. Check the VGA signal cable for the virtual or trailing characters, and focus on whether the ground wire of the RGB tricolor cable is connected normally - replace the screen cable or adapter board - rewrite the driver - replace the driver board - the signal interface IC of the LCD screen backplane is broken - the LCD screen backplane contrast potentiometer is adjusted - the LCD screen light guide plate is misaligned - the polarizer is misaligned. 7. Wipe or replace the protective film if there are stains inside the LCD screen - disassemble the screen body and clean the outer polarizer and organic glass (treated with cotton balls and purified water) - blow dry with an air blower. 8. One or two large bright spots on the LCD screen can be eliminated by pressing the bright spot gently with your fingertip, which means that most of the switching tubes and electrodes of this pixel are virtually connected.Small black spots and gray spots may be caused by dust on the internal light guide plate or polarizer, which can be cleaned. 9. Low LCD screen brightness Check the ADJ brightness adjustment circuit of the high pressure plate - change the lamp tube - change the high pressure plate - adjust or replace the light guide plate. 10. Error prompt out of frequency range Check signal line - Rewrite MCU driver - Replace EPROM - Rewrite EPROM program - Replace driver board. 11. After power on, if the switch button is not pressed, the white screen will appear backlight. The image after the button is pressed can normally display the switch signal of the high-voltage board interface and the ADJ signal are inversely connected, and some of the switch signals belonging to the MCU of the driver board are output abnormally. You can rewrite the MCU program to repair - replace the MCU. 2、 Switch power failure: 1. Fuse fusing For fuse fusing fault, usually check the filter capacitor in the main power supply rectifier filter circuit, each diode of the rectifier bridge and other components.Of course, when the anti-interference circuit has a fault, it will also cause the fuse to blow and blacken.It must be noted that the fuse blown due to switch tube breakdown is usually accompanied by the over current detection resistor and power control integrated circuit being damaged at the same time.Negative temperature coefficient thermistors are also easy to burn out together with the fuse, and attention should be paid to their inspection during maintenance. 2. There is no voltage output, but the fuse is not fused. There is no voltage output, but the fuse is not fused. This indicates that the switch power circuit is not working, or it has entered the protection state after working.During maintenance, first measure whether there is starting voltage at the starting pin of the power control integrated circuit. (1) If there is no starting voltage or the starting voltage is too low, check whether there is leakage between the starting resistor and the external components of the pin. (2) If there is starting voltage, then measure whether there are high and low jump level signals at the output end of the power control integrated circuit at the moment of starting·If there is no jump, it means that the power control integrated circuit itself or its peripheral oscillation circuit components or protection circuit are faulty. The method of replacing the power control integrated circuit first and then checking the peripheral components can be used to find the fault.If there is a jump, it is generally because the switch tube itself is poor or damaged, and it should be inspected emphatically. 3. In addition to the abnormal voltage stabilizing control circuit, there are usually three reasons for the low output voltage fault at the output end of the switching power supply caused by the low output voltage at the output end: (1) The performance of switch tube drops.This situation will lead to the switch tube not being able to conduct normally, making the internal resistance of the power supply larger and the capacity with load worse. (2) Rectifier diode and filter capacitor at output end fail.In this case, we can judge whether they are damaged by substitution. (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 all the loads of the switching power supply circuit can be used to distinguish between the poor switching power supply circuit or the fault of the load circuit.When the output voltage returns to normal after the load circuit is disconnected, it means that the load is too heavy;If it still fails to return to normal, it indicates that the switching power supply circuit is faulty. 4. If the output terminal voltage is too high, the output terminal voltage is too high, and most of the faults are in the voltage stabilizing sampling and voltage stabilizing control circuit of the switching power supply.Each component in the feedback loop composed of sampling resistor, error sampling amplifier, optocoupler, power control integrated circuit, etc. shall be checked.Usually, the sampling resistor is deteriorated, and the precision voltage stabilizing amplifier or optocoupler is damaged at a high rate.If the switching power supply with overvoltage protection circuit has excessive voltage, the overvoltage protection circuit can be disconnected first, and then the voltage on the main output terminal of the power supply can be quickly measured at the moment of startup. If the measured voltage is still higher than the normal value (generally higher than 1V, it is an over voltage fault), it should be repaired as per the above over voltage fault.
What is the reason why Xiaomi TV does not have a screen when it is turned on?The same is true of my Xiaomi TV. It's a bit stuck when I start watching videos. Suddenly, it starts flashing one day. You can try it and enter the Xiaomi TV set Set, select image and sound to enter, then select image parameters to enter, and select left image parameters to flip down to backlight, if it is 80-100% , and then it will continue to decrease until the screen is no longer blinking. At this time, the TV will be fine, the screen will not flash, and the TV will not be stuck.If the sudden flash is only shown on the fluorescent screen, and the accompanying sound is normal without interruption, then the fault is in the video amplifier circuit and the peripheral circuit of the picture tube, or even the possibility of electrode collision inside the picture tube is not ruled out, but when the voltage of the picture tube electrode collision or the acceleration electrode is too high, it will often be accompanied by a full screen flyback line; 2. If the image and accompanying sound disappear at the same time and return to normal soon, it is most likely that the scanning circuit or switching power supply part has faulty soldering, which is common in televisions that have been used for many years.
