Release date: 2010-08-24 Source: Projection Age
Biqiao Medical Technology(Henan)Co.,Ltd,Specializes
production,medical Masks,medical masks,surgical masks,KN95 masks,Kn95 Mask
reinforced,Disposable masks,children mask.Professional masks manufacturer.
Masks Protective Mask,3 Ply Face Mask,Disposable 3 Ply Face Mask,Medical Disposable Face Mask BIQIAO MEDICAL TECHNOLOGY(HENAN) CO.,LTD , https://www.medical-technology.net
With the wide application of liquid crystal displays on medical instruments and equipment, it is valuable and meaningful for medical equipment engineers to understand and master the common faults and maintenance of liquid crystal display units.
1. Characteristics and structure of liquid crystal display 1.1 Characteristics of liquid crystal display (1) Low voltage, micro power consumption: 2-3V can work.
(2) Flat-type structure: The basic structure of the liquid crystal display device is a thin-shaped case made of two glass substrates, which can accommodate a maximum amount of display content on a limited area, and the display content is most utilized.
(3) Passive display: The liquid crystal display device itself cannot emit light, and it modulates external light for display purposes. Therefore, there is no glare, no irritating to the human eye, and no eye fatigue. For the shortcomings that can't be seen in the dark, you can overcome it with a backlight.
(4) Large amount of information displayed: Compared with CRT, liquid crystal display devices have no shadow mask limitation, so pixels can be made smaller and finer; compared with plasma display, liquid crystal display device does not need plasma display at pixel points. That way, there must be a certain isolation area between pixels. Therefore, the liquid crystal display can accommodate more pixels and display more information within the same size display window area.
(5) Easy colorization: Although the liquid crystal itself is generally colorless, it is easy to colorize. Generally used are color filter and interference. Due to the maturity of the color filter technology, the colorization of the liquid crystal has a colorization effect that is more precise, more vivid, and has no color distortion.
(6) Long life: The liquid crystal material is an organic polymer synthetic material. It is of extremely high purity and other materials are also highly pure and manufactured under extremely clean conditions. The driving voltage of the liquid crystal is very low, and the driving current is extremely small. Therefore, the device has little deterioration and has a long life. From the actual application examination, in general use, in addition to impact, broken or damaged parts, the end of life of the liquid crystal display device itself is almost no (liquid crystal backlight life is limited, we generally refer to the life of the liquid crystal display mainly refers to the life of the backlight , but the backlight module is replaceable).
(7) No radiation, no pollution: The liquid crystal display device does not generate soft X-ray and electromagnetic wave radiation when used in the CRT. This kind of radiation not only pollutes the environment but also causes information leakage, and liquid crystal display does not cause such problems. It is ideal for personal safety and information confidentiality.
1.2 The basic structure of the liquid crystal display The structure of the common liquid crystal display. In terms of TFT-LCD, the key components include glass substrate, liquid crystal material, color film (color filter), polarizer, backlight module, driver IC, ICO conductive film. Wait. First, the light from the backlight is irradiated on the polarizer. After passing through the polarizer, the light is polarized, and the polarized light passes through the liquid crystal. Because the arrangement of the liquid crystal molecules is affected by the voltage generated by the electrode, the liquid crystal The polarizing angle of the polarized light can be changed, and the intensity of the light caused by different polarizing angles will be different. The light of different intensities will pass through the red, blue and green pixels of the color film, and will display various brightnesses and Different colors of pixels, and finally through the various pixels can form a variety of images and graphics that are visible to the naked eye. 2. Common faults of liquid crystal displays There is almost no degradation of liquid crystal display devices, and the life is very long. The backlight module is really determined by the life of the liquid crystal display. At present, the backlights used in liquid crystal displays are classified according to technology, mainly including tungsten halogen lamps, light emitting diodes (LEDs), organic electroluminescence (EL), cold cathode fluorescent lamps (CCFLs), cathode emission lamps (CLL), and metal halide lamps. . Among them, cold cathode fluorescent lamps are the most widely used, mainly because the performance, stability and cost of such backlights are better. Currently, almost all LCD displays use such backlights.
The author consulted some manufacturers' data and calculated that the life of cold cathode fluorescent lamps used in common liquid crystal displays is basically 30,000-50,000 hours. The outer diameter is 2.6-3.0 mm, the lamp voltage is 500-1000V, and the lamp current is 5mA. The lamp power is 0.5-7.0W and the starting voltage is 300-1500V. 3. Fault diagnosis and maintenance examples (1) Fault phenomenon: After the WELLDELL-sigma2000 portable ECG monitor is turned on, the power indicator light is on, the system self-test passes (the instrument emits a short “beepâ€), and the LCD display does not display any The instrument works normally.
(2) Fault analysis and overhaul: The power indicator light is on, indicating that the power supply is normal. The system self-test passed, indicating that the CPU and memory are not damaged. There is no display during the LCD self-test, which can preliminarily eliminate the possibility of system software damage. There is no hardware alarm sound, the instrument works normally, indicating that the hardware part should be undamaged. Observing the liquid crystal display under the side light, the system software operation interface is faintly visible. The preliminary analysis is that the backlight module is faulty.
Open the case, after the power is turned on, the light guide plate is not lit, you can conclude that the backlight module is faulty. The main components of the backlight module are observed as a backlight tube, a high voltage circuit board, a light guide plate, and the like. Because the liquid crystal display unit is precise, the independent high-voltage circuit board is first diagnosed. The low-voltage DC input terminal of the circuit board is connected to the instrument main board, and the high-voltage AC output terminal is connected to the backlight tube. Under the power-on state, the low-voltage DC input is 11.5V, and the high-voltage AC output is 650V with the multimeter 2500V gear. (Because the circuit board is mostly long and narrow, be careful to prevent the test leads from being short-circuited when measuring.) This shows that the high voltage circuit board is working properly. Next, check the backlight tube, first open the back metal shell of the liquid crystal display unit (the liquid crystal display unit of some instruments uses an insulating adhesive tape on the back, whether it is a metal shell or an insulating adhesive paper, in order to use the glass substrate and the liquid crystal The outer frame of the display unit is fixed as a whole. At this time, the metal groove for fixing the backlight tube can be taken out, and the lamp tube is carefully removed from the metal groove (because the outer diameter of the backlight tube is mostly 2.6-3.0) Mm, very easy to break, so be careful). At this time, the lamp still does not light up after starting up (this step is to quickly determine whether the lamp is damaged. If the lamp is illuminated, the lamp is not damaged, the only possible failure is the short circuit or open circuit at both ends of the lamp) After the power is off, observe the casing wrapped at both ends of the lamp (to prevent the terminal from being exposed) without wear or aging. Then cut the casing and observe that the terminal is not broken or soldered. Further detecting the wire connecting the high voltage output terminal and the lamp terminal, the result is normally turned on. At this time, it can be finally determined that the cause of the failure is damage or aging of the backlight tube. Backlight tube manufacturing process is high, generally need to be purchased from the manufacturer. But because of the inconvenience of transportation and long delays,
I chose the laptop display backlight tube that is relatively easy to buy. The sigma2000 ECG monitor uses the 10.4†LCD produced by NEC, and its lamp is placed on the long side of the display, while most laptops The tube is placed on the short side of the display. After measuring the length, it can be replaced with a 13.3" LCD notebook tube. After the replacement, the lamp is normally illuminated and the fault is solved. 4. Other common faults and fault diagnosis process of LCD monitor In addition to the fault of the backlight tube damage or aging, the author has encountered some other fault conditions in the repair work:
(1) High voltage circuit board failure;
(2) The casing of the backlight tube is worn at both ends, causing the terminal to be exposed, causing a short circuit in contact with the metal groove;
(3) The backlight tube terminal is disconnected, causing an open circuit.
On this basis, the author summarizes the fault diagnosis process of a liquid crystal display. 5. Conclusion The excellent characteristics of liquid crystal display devices determine its position in various display devices. The backlight module is almost the only factor limiting its life. However, some well-known manufacturers have studied and initially improved the backlight module. It is believed that with the gradual improvement of liquid crystal display technology and the continuous reduction of production costs, it will eventually replace the traditional CRT and become a technology closely related to people's lives.