Brief introduction of common malfunction maintenance of liquid crystal display

1. Monitor machine without voltage

(1) Power failure: This is a very simple fault, the general LCD display extension inside the power supply and external power supply two, outside the common some. Regardless of that power supply, its structure is much simpler than the CRT monitor's power supply, and is usually vulnerable to a number of small components, such as the safety pipe, Rectifier bridge. 300V filter capacitor, power switch, power management IC, rectifier output diode, filter capacitor, etc.

(2) Driver board failure: the driving plate burning insurance or voltage regulator chip failure, there are some of the machine is the switching power supply built-in, output two sets of power supply, including a group of 5V, for signal processing, and another group is 12V to provide high-voltage plate point backlight, If the switching power supply part of the circuit failure will likely cause two groups of power supplies are not output. First check the 12V voltage is normal, and then check the 5V voltage is normal, because a/D driver Board MCU chip operating voltage is 5V, so find the failure of the machine, first use a multimeter to measure 5V voltage, If there is no 5V voltage or 5V voltage becomes very low, then one may be the power circuit input level problems, that is, 12V to 5V power supply part of the problem, this fault is very common, check 5-terminal voltage regulator block (common model 8050sd-lm2596-aic15-01, etc.)

Another possibility is that the 5V load is heavier, the 5V voltage is pulled very low, in other words, it is said that the signal processing circuit after the problem, some of the circuit damage, resulting in heavier load, the 5V voltage pull very low, one after another to troubleshoot the problem of components, replace the defective components, 5V can return to normal, Trouble is generally resolved, also often encountered 5V voltage back to normal after the normal boot, this situation also has a variety of reasons, on the one hand, the MCU program is flushed may cause no boot, there is the MCU itself damaged, such as the MCU I/O port damage, so that the MCU can not scan the key, Encountered this fault caused by the MCU, look for hardware problem is no use, even if you changed the MCU can not solve the problem, because the MCU is required to program and write code, in the absence of a way to find the original AD driver board replacement, we can only use a general-purpose A/D driver board substitution, such as: 151D or 161B.

2. The display will not light up, but the power indicator light is always on.

This problem is usually caused by high pressure, is the protection of the circuit action, in this case, the general LCD screen is displayed, see the method is "strabismus."

Overhaul 2 of the method can be a single lamp high pressure plate after a lamp test, because, now the LCD display of high-pressure board design is generally symmetrical design, and both sides of the bad may be basically not. The general old machine is prone to problems is a certain way of the power tube, step-up tube, step-up transformers and tubes short-circuit or no-load, and the resulting power management IC load balance protection. See the high pressure board interface has so many lines, many beginners think that the replacement is very complex, in fact, it is very simple, only need 4 signal received high-voltage plate can: 1, power. 2, ground. 3, switch control On/off. 4,adi brightness adjustment. First determine the power line positive and negative, the general is the cathode, the cathode is connected to the capacitor of the cathode. Then determine the voltage, the best way to determine the voltage is to look at the capacitance of the mark, if the 6V or so is 3.3V, if the capacitance superscript 12V or so, Then the input voltage must be 5V, if it is about 24V or more, then it is 12V, by analogy, the number of volts on the capacitor is divided by two, the closest to a few volts is a few volts. Some people say that by this way, or not bright, or just flash it out, yes there are many high pressure board is such, how to do? Find the control foot and see if the foot is attached to a small transistor, generally direct to the transistor, the most middle there is a small capacitor, it should be easy to identify, the control foot is generally 3.3V and 5V, there are individual is grounded, so we do not know the case, the first grounding to try, No, then 3.3V and then 5V, if the input voltage and control voltage is 3.3V, can be directly merged. What about the extra feet? Let him be free, and ignore it.

3. Screen black screen, no backlight. Power light green illuminated steady.

Strabismus LCD display image, many belong to the High-voltage plate power supply circuit problems. Focus on checking 12V power supply (fuse f) and 3V or 5V switching voltages are normal. If the MCU problem caused no output switch control voltage, can directly extract 3-terminal voltage Regulator block (AIC1084) 3.3V instead. The idea of repairing high pressure plate (power fuse----switch control tube----power management IC----push-pull tube----POWER switch----DA conversion circuit (energy-storing inductor, rectifier)---LC step-up Circuit (step-up transformer, step-up capacitor)------coupling capacitor- ---tube.

4. Screen light line, light band or dark lines

This problem is generally the LCD screen failure.

Light line failure is generally connected to the LCD screen body of the line out of the problem or a row and column of the driver IC damage.

Dark line is generally the body of the screen has leakage, or tab flexible plate wiring open. The above two kinds of problems are basically to the machine sentenced to death, there is no maintenance value, because a screen price is too high.

5. Flower screen or screen

This problem is generally the screen of the driving voltage out of the problem, first change the drive plate and drive screen test, if not check the screen backplane power supply circuit, maintenance ideas: drive plate 5V to 3.3V of the voltage Regulator block (AIC1084) whether there is power output.---screen body drive plate fuse (F)-3.3V----- DC Converter Circuit----negative pressure forming IC ( -7v)----row, column drive IC.

6. Partial Color fault

Can generally enter the factory adjustment mode for adjustment. If there is no such mode, maintenance ideas: Replacement screen and transfer board-----Rewrite the driver-----The driver board bad (uncommon)-----screen backplane control IC bad (uncommon)--------unplug the screen to observe the backlight color (backlight flat color for the lamp aging)-------Change the lamp.

7. Character false or trailing

Maintenance idea: Check the VGA signal line, Focus on the r.g.b of the three-color line is connected to the normal-----replace the screen or the switch board-----rewrite the driver-----change the driver board----LCD Screen backplane signal interface IC Bad-----LCD screen backplane contrast potentiometer adjustment------LCD Screen plate dislocation----polarizer dislocation

8.LCD screen has a stain inside.

Maintenance idea: Wipe or replace the protective film-----disassemble the screen body to clean the outer polarizer and plexiglass (with cotton balls, purified water treatment)---blow dry

9.LCD screen leaky or uneven light

Maintenance idea: Reinstall the lamp-----Adjust the guide plate

10:LCD Screen Highlights

One or two big bright spots, you can try to gently use your fingertips to press the bright spot, can disappear, the description of many of the pixels of the switch tube and electrode virtual connection. Small black spots and grey dots may be caused by dust in the interior guide plate or polarizer. Can be cleaned and treated.