LCD Screen Use And Troubleshooting

- Aug 27, 2018-




(1). Use of LCD: Due to the special principle and structure of the liquid crystal display device, it must be noted when using the installation:

1. Preventing excessive pressurization: The liquid crystal display device is a liquid crystal cell made of two sheets of glass. There is only 5~10um between them, and the inner surface of the glass is also coated with an orientation layer, which is easy to break. Therefore, attention should be paid during assembly and use:

A. The surface of the LCD should not be over pressurized to avoid damaging the alignment layer. If the pressure is too large, or if the middle of the LCD is pressed by hand, it should be placed for at least 1 hour before being powered.

B. Remember to make the pressure uniform in the assembly, only press the edge of the device, can not press the middle, and can not force unevenly.

2. Prevent glass breakage: Since the LCD is made of glass, if it is lost or impacted, it will definitely cause cracking. Therefore, the assembly method and the vibration and impact resistance of the assembly must be considered in the design of the whole machine.

3. Protective pin: If it is a pin-type LCD, the LCD should be installed 2mm or more away from the line board, and it should not be subjected to excessive force and heat, so as not to damage the connection. The maximum temperature resistance at the joint must not exceed 80 °C. Do not use detergent at the pin, as washing in the daylight will decompose C12, and after water absorption, hydrochloric acid will form to corrode the electrode.

4. Device moisture:

Since the LCD is low voltage, micro power consumption, the liquid crystal material has a very high resistivity (up to 101oΩ.cm or more). Therefore, the surface of the glass due to moisture is conductive enough to affect the display. A "crosstalk" display will occur between segments. Therefore, the design of the whole machine should consider moisture-proof, the chassis is well sealed, and even a sandwich-type conductive rubber strip is used.

5. Preventing scratches and pollution: Since the surface of the liquid crystal display device is a plastic polarizer, it is absolutely necessary to avoid scratching and staining of hard krafts during assembly and use. There is a protective film on the polarizer on the upper surface of the LCD to avoid scratches and stains. When assembling, the protective film should be removed when the final assembly is completed. Even so, it is best to wear cotton gloves during installation and operation to avoid stains such as sweat, oil, and cosmetics. If it has been stained, it should be wiped with a fine cloth or cotton ball in time; if it is too heavy to be cleaned with solvent, it can only be wiped with isopropyl alcohol (glycerin), alcohol, freon, and dried quickly, but must not Use acetone, aromatic solvents (such as toluene and water and scrub), otherwise it will damage the LCD surface polarizer.

6. Prevent the application of DC:

The smaller the DC component of the driving voltage, the better, preferably not exceeding 50 mV. Applying an excessive DC component for a long time causes the electrode to undergo an electrochemical reaction and deteriorate. In the segment display, a divide-by-2 circuit is often introduced in the oscillating circuit to ensure the symmetry of the square wave.

7. UV protection: Both liquid crystal and polarized light are organic substances, which cause photochemical reactions under the ultraviolet light to cause deterioration. Therefore, it should be considered according to the conditions and environment of the LCD whether it is necessary to install an anti-ultraviolet filter.

8. Use and storage within the specified temperature range: Since the liquid crystal state will disappear beyond a certain temperature range, it must be used and stored in the specified temperature range. When the temperature is too high, the liquid crystal state disappears and becomes an anisotropic liquid, and the display is black and cannot work. Do not apply power at this time. When the temperature returns to normal, the display surface will return to normal. If the temperature is too low, the liquid crystal state will also disappear and become a crystal. At this time, it is possible to damage the orientation layer during the crystal process and cause permanent damage.

9. Electrostatic interference: Since the LCD operating voltage is extremely low and the internal resistance is very large, when using a multimeter (x10K file), the phenomenon of "string" sometimes occurs. This is due to the suspension of the electrode, which is a normal phenomenon.

(2). Elimination of faults in use: When a qualified display device is used, it may sometimes malfunction due to unreasonable use, unsuitable conditions, and failure of accessories or improper installation methods. The reasons and exclusions are as follows:

1. Handwriting exclusion: After a few hours or a few days, the electrode will appear black and brown "writing", and the liquid crystal box will generate bubbles, which will make it impossible to display. This is caused by the fact that the DC component of the driving voltage is too large, causing an electrochemical reaction. Check the circuit, remove the large DC component, and replace it with a new LCD. When the “writing” appears, the LCD can be heated to above the temperature, that is, when the display surface of the display device is completely discolored, the temperature rise is stopped, and after the natural cooling, the “writing” can be generally removed.

2. Vaguely displayed: the pen segment that should not be displayed after assembly is also faintly displayed, so that it cannot be read. The reason may be:

A. The lead is not clean, just wipe it with a dry cloth;

B. The weather is too humid, the surface of the glass is conductive, and it can be restored after drying indoors;

C. The common electrode or the segment electrode is suspended, and after re-assembly is reliable, it can be eliminated;

D. The amplitude of the AC square wave is asymmetrical, which causes the cutoff to be unclear when it is extinguished, and the square wave amplitude can be adjusted.

E. When the conductive rubber stripe is not square, non-parallel, and the insulation performance is poor, the conductive rubber may be replaced long;

3. Exclusion of contrast difference: poor contrast, or negative image, or display confusion, or all display, generally due to the back electrode floating, can be eliminated.

4. Exclusion of confusion display: External interference may also cause display confusion, and it can be eliminated.

5. Exclusion of all displays: The decoder is normal, but all display, generally the back electrode is not connected, or the back electrode appears DC.

6. Exclusion of the missing outline: The reason for the missing display may be:

A. Contamination of the electrode leads, resulting in poor assembly contact;

B. Contamination of conductive rubber, resulting in poor assembly contact;

The above two items only need to be cleaned, and the parts to be cleaned cannot be touched by hand.

C. The edge of the glass is broken, and the outer lead conductive layer is scratched;

D. The assembly press frame is unqualified;

7. Exclusion of random display: The cause of disorder display may be: back electrode floating, driving to DC, power fluctuation, poor contact, battery exhaustion, etc. can be excluded according to different reasons.

8. Intermittent display exclusion: dysfunction, can not be adjusted, the reason is that the power supply voltage is not normal, the battery is exhausted, you need to replace the battery at this time.

2. Module troubleshooting: In order to troubleshoot, first of all, have a certain understanding of the module, so that the module can be repaired with half the effort.

(1). Prerequisites for troubleshooting:

1. In order to assemble the module, you need to have some understanding of the principle of the module, so that there will be a problem after the module is assembled. For example, when two SEG electrodes are on one chip pin control panel on the PCB board, once two SEGs are missing from the symmetry of the module, it can be concluded that the PCB board is a problem.

2. Have a certain understanding of the composition of the module. A module, in order to have a good electrical display, shell, screen, zebra strips, PCB board must be designed reasonably, raw materials qualified to receive good results. Such as: zebra strip compression ratio is not enough, resulting in lack of stroke, this situation is repeated assembly, reliability is not good, then it is necessary to change the zebra strip.

3. To master certain assembly skills, master certain skills in troubleshooting, you can be handy and reduce assembly problems.


(2). Simple troubleshooting:

1. Show confusion for exclusion:

A. Misalignment: PCB board electrodes and screen electrodes cannot be one-to-one correspondence. At this time, the cause of the misalignment should be analyzed.

a. Due to the assembly problem in the assembly, it is necessary to reassemble.

b. The PCB mounting holes are not in the correct position.

c. The edge of the screen is not accurate.

d. The shell alignment is not accurate.

B. The PCB board is broken. At this time, the test board tooling can be used to test the board again.

External interference may also cause display confusion, and then detect external interference and eliminate it.

2. Exclusion of missing outlines:

A. The PCB board electrodes are contaminated, resulting in poor contact of the zebra strips.

B. The zebra strips are contaminated, resulting in poor contact.

C. The lead electrode is contaminated, resulting in poor contact.

The above three items only need to be cleaned and reassembled. When assembling, do not touch the cleaned parts with your hands.

D. PCB board breakage, virtual soldering. Re-test the board once, if it is bad, change the board.

E. The screen electrode is broken or the screen is broken or shorted. Need to change screen and reassemble.

F. The shell failed and the shell was assembled again.

3. Display all or no black: This situation is generally a problem with the PCB board, and the PCB board needs to be re-measured after disassembly.

4. Uneven, shallow bars: This situation can only be ruled out if he analyzes it carefully.

A. The module is not evenly displayed but the wiring is not neat. This situation is generally the reason for the screen, reassembled after the update.

B. Some of the displays are uneven. In this case, the zebra strip is generally distorted, resulting in poor contact. After the removal is required, the zebra strips are laid flat and assembled again. If it can't be ruled out, it is necessary to analyze other reasons, such as the zebra strip height and width ratio are not suitable, the compression ratio is not suitable, and the conductive bandwidth is not suitable.

C. The PCB board is slightly soldered. Remove the PCB board, measure the PCB board, and reassemble.

5. Half deep and half shallow, no program, abnormal program, less screen or a few screens, no timing, shadows, etc.

This phenomenon is generally a problem with the PCB board. It is necessary to remove the PCB board to measure the PCB board. Reassemble with a good PCB.