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>> Use and troubleshooting of LCD with TFT-LCM simple troubleshooting 28th,Apr,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) Prevent excessive pressure:
The liquid crystal display device is a liquid crystal cell made of two sheets of glass, only 5 to 10 μm between them, and the inner surface of the glass is also coated with an orientation layer, which is easy to destroy. Therefore, attention should be paid to the assembly and use of the liquid crystal display device.
The surface of the LCD should not be over-pressurized so as not to damage the alignment layer. In the event that the pressure is too great, or if you press the middle of the LCD with your hand, you must put it on for at least 1 hour before turning on the power.
It is important to keep the pressure even in the assembly, press only the edge of the device, not the middle, or even the force.
(2) Prevent glass breakage:
Since the LCD is made of glass, if it is lost or impacted, it will certainly cause cracks. Therefore, in the design of the entire machine, the assembly method, vibration resistance and impact resistance of the assembly must be considered.
(3) Prevent the application of direct current:
The smaller the DC component of the driving voltage, the better. It is better not to exceed 50mV. Applying excessive DC components for a long time will cause the electrode to electrochemically react and age. In the segment display, a frequency dividing circuit is often introduced in the oscillation circuit to ensure the square wave symmetry.
(4) Device moisture protection:
Since the LCD is low-voltage, micro-power-consumption, and the liquid crystal material has extremely high resistivity (up to 1010 Ω.cm or more), the conductivity of the glass surface due to moisture is enough to affect the display. There will be a "crosstalk" display between the segments. Therefore, the design of the whole machine should consider the moisture proof, the enclosure is good, even the sandwich type conductive rubber strips.
(5) Protection pins:
If it is a pin-type LCD, the LCD should be installed 2mm or more away from the board, and it must not be subjected to excessive force and heat, so as not to damage the connection. The maximum temperature at the connection must not exceed 80°C. Do not use detergents on the pins, because the detergent will decompose Cl2 in the sunlight and absorb hydrochloric acid to erode the electrodes.
(6) Use and storage within the specified temperature range:
Since the liquid crystal state disappears beyond a certain temperature range, it must be used and stored within the specified temperature range. If the temperature is too high, the liquid crystal state disappears and the liquid becomes isotropic. The display surface is black and does not work. Do not power on at this time. When the temperature returns to normal, the display will return to normal. If the temperature is too low, the liquid crystal state disappears and becomes crystalline. At this point, it is possible to destroy the orientation layer and cause permanent damage during the formation of crystals.
(7) UV protection:
Both liquid crystals and polarizers are organic substances, and photochemical reactions are generated under ultraviolet irradiation to deteriorate them. Therefore, it is necessary to consider whether or not to install an ultraviolet filter in accordance with the conditions of use of the LCD and the environment.
(8) Prevent scratches and contamination:
Since the surface of the liquid crystal display device is a plastic polarizer, assembly and use should absolutely avoid scratching and contamination of hard objects. The surface polarizer on the LCD has a protective film to avoid scratches and stains. When assembling, the protective film should be removed when the final assembly is completed. Even so, when installing and operating, it is best to wear cotton gloves to prevent hand sweat, oil stains, cosmetics and other contamination. If it has been contaminated, it should be timely wiped with a fine cloth or cotton ball; if it must be washed with solvent when it is too heavy, it can only be wiped with isopropyl alcohol (glycerin), alcohol, or freon, and it should be dried quickly, but it must not be dried. Use acetone, aromatic solvents (such as toluene and water scrub), otherwise it will damage the LCD surface polarizer.
(9) Electrostatic interference:
Since the LCD has a very low operating voltage and a large internal resistance, when using a multimeter (×10K file), a “string” phenomenon sometimes occurs. This is due to the floating of the electrode and is a normal phenomenon.
<2> Troubleshooting in use:
When a qualified display device is used, it sometimes fails due to unreasonable use, unsuitable conditions, and unqualified accessories or improper installation methods. The reason and exclusion are as follows:
(1) Handwriting elimination:
After hours or days of use, the electrodes are discolored with black and brown "writings", and the liquid crystal cell generates bubbles that prevent it from being displayed. This is because the DC component of the driving voltage is too large, causing an electrochemical reaction. Check the circuit and remove the excessive DC component. Then replace it with a new LCD. When the “writing” has just appeared, the LCD can be heated to above the guaranteed temperature. When the display surface of the display device is completely discolored, the temperature rise is stopped. After the natural cooling, the “writing” can be generally removed.
(2) Vaguely displayed:
Pens that are not supposed to be displayed after assembly are also displayed vaguely so that they cannot be read out. The reasons may be:
1 When the conductive rubber stripe is not correct, is not parallel, and the insulation performance is poor, replace the conductive rubber strip.
2 The asymmetry of the amplitude of the alternating square wave up and down, resulting in unclear when the extinguished, can be solved by adjusting the square wave amplitude.
3 If the common electrode or segment electrode is left unconnected and the reassembly is reliable, it can be eliminated.
4 The weather is too hot, the surface of the glass is conductive, and it can be restored after the interior is dry.
5 The lead is not clean, use a dry cloth to wipe the cloth.
(3) Exclusion of poor contrast:
Contrast is poor, or negative images appear, or display confusion, or all displayed, generally due to the back electrode floating caused by exclusion.
(4) Exclusion of missing display:
The reason for the missing display may be:
1 Electrode lead contamination, resulting in poor assembly contact.
2 Conductive rubber stained, resulting in poor assembly contact.
The above two items only need to be cleaned and assembled, and the cleaned parts cannot be touched by hand during assembly.
3 The edge of the glass is broken, scratching the outer lead conductive layer.
4 Assembly pressure frame failed.
(5) Exclusion of intermittent display:
The function is disordered and cannot be adjusted because the power supply voltage is abnormal and the battery is exhausted. At this time, the battery needs to be replaced.
(6) Exclusion of all displays:
The decoder is normal, but all are displayed. Generally, the back electrode is not connected, or the back electrode appears DC.
(7) Exclusion of confusion display:
External disturbances may also cause confusion and exclusion.
(8) Exclusion of chaotic display:
The cause of the chaotic display may be: the back electrode is floating, the drive is DC, the power supply is fluctuating, the contact is bad, the battery is exhausted, etc. may be excluded according to different reasons.
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