I. Use of LCD:

Due to the special principle and structure of liquid crystal display, attention must be paid when using and installing:

(1) Prevent excessive pressure:

The liquid crystal display is a liquid crystal box made of two pieces of glass, with only 5-10um between them. The inner surface of the glass is also coated with orientation layer, which is easy to destroy. Therefore, attention should be paid in assembly and use:

The surface of LCD should not be pressurized too much, so as not to destroy the orientation layer. In case of excessive pressure, or pressing the LCD center by hand, it should be placed for at least 1 hour before energizing. The assembly must be with uniform pressure only at the edge of the display, not in the middle.

(2) Prevent glass damage:

As LCD is made of glass, it will certainly cause rupture by fall and impact, so the assembly method must be considered in the design of the whole machine, such as the assembly of vibration and impact resistance performance.

(3) Prevent direct current from being applied:

The smaller the direct current of the driving voltage is, the better if it’s not more than 50mV. Too much DC applied for a long time will cause electrochemical reaction and aging of the electrode. In the segmenting display, the divide-frequency circuit is often introduced into the oscillating circuit to ensure the symmetry of the square wave.

(4) Prevent moisture: as the LCD is low voltage, micro power consumption, high resistivity of liquid crystal materials(more than 1010Ω. Cm), the conductive glass surface caused by moisture will affect the display performance. A "crosstalk" display will occur between the segments. Therefore, the design of the whole machine should consider moistureproof, good sealing of the case, and even the use of interlayer conductive rubber strip.

(5) Protect the PINS: If it’s a PIN type LCD, the LCD shall be installed 2mm or further away from the PCB, and it shall not bear too much force or be heated too high, so as to avoid damaging the connection. The maximum temperature at the junction shall not exceed 80℃. No detergent should be used at the PIN, because the detergent will decompose Cl2 in sunlight and form hydrochloric acid to corrode the electrode after water absorption.

(6) 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 within the specified temperature range. If the temperature is too high, the liquid crystal state will disappear and become the isotropic liquid, the display will be black and cannot work. Do not electrify at this time, when the temperature returns to normal, the display will return to normal too. If the temperature is too low, the liquid crystal state will disappear and become a crystal. It is possible to destroy the orientation layer during crystal formation and cause permanent damage.

(7) Anti-UV light: liquid crystal and polarizer are organic matter, which will produce photochemical reaction under UV irradiation and degrade them. Therefore, it is necessary to consider whether an anti-UV filter is needed according to the use conditions and environment of LCD.

(8) Prevent scratch and pollution: since the surface of liquid crystal display is plastic polarizer, the assembly and use should absolutely avoid scratch and contamination with hard objects. The surface of LCD polarizer has a layer of protective film, so as not to cause scratches, contamination. The protective film should be peeled off when the final assembly is completed. Even so, in the installation and operation, it is best to wear cotton gloves to avoid hand sweat, oil, cosmetics and other contamination. If it has been stained, it should be promptly swabbed with muslin and cotton ball. If the stain is too heavy and must be cleaned with solvent, only isopropyl alcohol (glycerin), alcohol and freon can be used, and acetone, aromatic solvent (such as toluene and water scrub) are never allowed to use, otherwise it will damage the polarizer on the LCD surface.

(9) Electrostatic interference: due to the working voltage of LCD is very low, the internal resistance is very large, so in the use of multimeter(x10K) inspection, sometimes there will be "string" phenomenon, this is due to the electrode suspension, and it’s a normal phenomenon.

II. Troubleshooting in use:

When a qualified display is in use, it will sometimes fail due to unreasonable use, inappropriate conditions, unqualified parts or improper installation methods. The reasons and elimination methods are as follows:

(1)Handwriting elimination: after a few hours or days of use, black and brown "handwriting" will appear when the electrode discoloration, and bubbles will be generated in the crystal box, resulting in the inability to display. This is due to the DC of driving voltage is too large, resulting in electrochemical reaction. Check the circuit, remove the excessive DC, replace the new LCD. When the "writing" just appears, the LCD can be heated to the guaranteed temperature above, that is, when the image of the display is all discolored, stop heating, and after natural cooling, the "writing" can generally be removed.

(2)Vague indication: the segment that should not be displayed after assembly is vague, so that it cannot be read out. The reason may be:

① The conductive rubber stripes is skewed and not parallel, the insulation performance is poor, just replace the conductive rubber strips.

② The amplitude of AC square wave at up and down is asymmetric, resulting in the cutoff is not clear when powered off, adjust the amplitude of square wave and it can be solved.

③ Public electrode or segment electrode suspended, just re-assemble and it can be eliminated. ④ The weather is too damp, the surface of the glass is conductive, dry in the room and it can be restored.

⑤ lead wire is not clean, just wipe with dry muslin

(3)Elimination of the poor contrast: the contrast is very poor, or there is a negative image, or display confusion, or all display, it’s generally caused by the back electrode suspension, just eliminate it.

(4)Elimination of the line defect. The reason of the line defect may be:

①Electrode lead is stained, resulting in poor assembly contact.

②Conductive rubber contamination, resulting in poor assembly contact.

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

③The glass edge is damaged and the conductive layer of the external lead is scratched.

④Assembly of pressure frame is not qualified.

(5)The elimination of intermittent display: the function is disordered and cannot be adjusted. The reason is that the power supply voltage is abnormal and the battery is exhausted. At this time, the battery needs to be replaced.

(6)The elimination of all display: the decoder is normal, but all display, generally it’s the back electrode is not connected well, or the back electrode appears DC.

(7)The elimination of display of chaos: external interference may also cause the display of chaos, just eliminate.

(8)The elimination of disordered display: the reasons for disordered display may be: the back electrode is suspended, or the drive voltage is DC, or the power supply fluctuation, or bad contact, or battery exhaustion, etc., it can be eliminated according to different reasons.