Maintenance methods for common faults of smart LCD TVs
April 1, 2022
The smart TVs at home will have small problems of one kind or another after a period of use. Some of them can be repaired by themselves, and they will be sold without knowing it.
First, determine the fault:
To repair the LCD, you must learn to judge which part is faulty. This is the first step. Let's talk about the main faults of LCD TVs and the judgment of their parts.
1: There is no image and no sound when booting, the power light flashes and turns to be always on, and the screen flashes white light at the moment of booting. This fault is mostly the damage of the backlight driver board. However, in the maintenance, I have also encountered damage to the lamp tube in the screen .
2: The screen is blurred (mosaic) after booting for one time, and the sound is normal. The first phenomenon is that the digital board is not good (the via hole is not connected or the IC contact is not good). The second is that the internal connection of the machine is not in good contact.
3: There are three no power on, the power light is not on, the first is that the power supply board is broken, and the second is that the CPU part is not working properly.
4: The light flashes and cannot be turned on: the CPU bus is not working properly or the boot program IC (BIOS) is bad, and the contact between the "BIOS" IC and the CPU is poor.
Second, maintenance ideas:
1. The monitor has no electricity
(1) Power failure: This is a very simple failure. Generally, there are two kinds of power supply inside the LCD display extension machine and external power supply, and the ones outside the machine are more common. No matter what kind of power supply, its structure is much simpler than the power supply of crt display, and the vulnerable components are generally some small components, such as fuse, rectifier bridge, 300V filter capacitor, power switch tube, power management IC, rectifier output diode, filter capacitors, etc. The commonly used ic for the power board: 6841 203d06, these commonly used pmw chips can be bought in professional LCD accessories stores like me.
(2) Failure of the driver board: the driver board burns the fuse or the voltage regulator chip fails. Some machines have built-in switching power supplies and output two sets of power supplies, one of which is 5V for signal processing, and the other is 12V. The high-voltage board is used for backlighting. If there is a fault in the switching power supply part of the circuit, it may cause the two sets of power supplies to not output. First check whether the 12V voltage is normal, and then check whether the 5V voltage is normal, because the MCU chip of the A/D driver board works. The voltage is 5V, so when looking for the fault that cannot be turned on, first measure the 5V voltage with a multimeter. If there is no 5V voltage or the 5V voltage becomes very low, then one possibility is that there is a problem with the input stage of the power supply circuit, that is to say, the 12V conversion There is a problem with the power supply to 5V, this kind of failure is very common, check the 5-terminal voltage regulator block (common model 8050SD-LM2596-AIC15-01, etc.).
One possibility is that the 5V load is aggravated, and the 5V voltage is pulled very low. In other words, there is a problem with the signal processing circuit of the rear stage, and some circuits are damaged, causing the load to increase, and the 5V voltage is pulled very low. Low, check the faulty components one by one. After replacing the faulty components, 5V can return to normal, and the fault is generally solved. It is also often encountered that the 5V voltage cannot be turned on normally after returning to normal. There are also many kinds of situations. The reason is that on the one hand, the program of the MCU is washed out, which may lead to the failure to 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. It is useless to find the problem of hardware, even if you change the MCU, it will not solve the problem, because the MCU needs to be programmed and written, and in the case that there is no way to find the original AD driver board to replace, we can only use the general A /D driver board replacement such as: 151D or 161B, etc.
2. The display does not light up for a while, but the power indicator light is always green.
This kind of problem is generally caused by abnormal high voltage, which is the action of the protection circuit. In this case, there is usually a display on the LCD screen, and the way to see it is to "squint".
3. The display screen is black, no backlight. The power light is always green.
If there is an image displayed on the squinting LCD screen, it is mostly a problem of the power supply circuit of the high-voltage board. Focus on checking whether the 12V power supply (fuse F) and the 3V or 5V switching voltage are normal. If there is no output switch control voltage due to the MCU problem, you can directly extract the 3-terminal stable voltage Compression block (AIC1084) 3.3V instead. The idea of repairing the high voltage board (power fuse----switch control tube----power management IC----push-pull big tube----power switch tube-- --DA conversion circuit (energy storage inductor, rectifier tube)---LC boost circuit (boost transformer, boost capacitor)------coupling capacitor----lamp tube.