Monitor black screen and image distortion troubleshooting

A liquid crystal monitor, that is, a liquid crystal display, is a flat, ultra-thin display device consisting of a certain number of color or black and white pixels placed in front of a light source or a reflective surface. Liquid crystal displays consume very little power and are therefore favored by engineers for use in electronic devices that use batteries. Its main principle is that current stimulates liquid crystal molecules to generate points, lines, and planes with the back lamp to form a picture. At this stage, with the popularity of LCD splicing, several common problems are apparent.

Black screen troubleshooting method

What are the causes of black screen failure on the LCD monitor?

The first is the power circuit is not good caused by: the performance of the panel buttons without any reaction, the indicator light is not bright, first check the 12V voltage is good or not, followed by check 5V voltage is good, because the A/D driver board signal processing part of the chip work The voltage is 5V, so when the fault can't be detected, first use a multimeter to measure 5V voltage. If there is no 5V voltage or 5V voltage becomes very low, then there may be a problem in the input stage of the power circuit. There was a problem with the 12V to 5V power supply.

This kind of fault is very common, usually burn insurance or voltage regulator chip failure, some of the machine is the built-in switching power supply, output two sets of power, one set is 5V for signal processing, the other set is 12V to provide high voltage For backlighting on the board, if there is a fault in the circuit of the switching power supply, it may result in no output of both sets of power supplies.

Another possibility is that the 5V load is getting heavier, and the 5V voltage is pulled very low. In other words, the signal processing circuit in the rear stage has a problem, some of the circuits are damaged, the load is aggravated, and the 5V voltage is pulled. Very low, one by one after the investigation of the problem of the components of the latter stage, after replacing the faulty components, 5V can recover well, the fault is generally resolved, but also often encountered 5V voltage recovery can not be a good boot.

There are many reasons for this situation. On the one hand, the MCU program may be washed out, which may cause no boot. There is also damage to the MCU itself. For example, the I/O port of the MCU is damaged and the MCU cannot scan the keys. Faults caused by the MCU, find the hardware problem is useless, even if you change the MCU can not solve the problem, because the MCU is the need to program and write the Ma, in the case of no way to find the original AD driver board replacement, We can only find another way to find the A/D driver board that can be replaced. There are many places on the market that can be purchased. If the local market can't buy it, you can post it on the LCD home forum. Many LCD masters may be able to purchase the accessories you need and find the information you need.

The distortion of the monitor image distortion

1. When the LCD monitor is used as a monitor terminal of a matrix control system, why does the matrix controller switch the image for a while?

In the monitoring system, if there is a phase difference between the field sync signals in the image signals output from each front-end device (such as a camera), the monitor will display a period of non-synchronization when the matrix controller switches the image signals of each channel. The larger the phase difference, the longer the time that is not synchronized. Therefore, it is recommended that when constructing a monitoring system, front-end devices with GEN-LOOK inputs should be used as much as possible, and all front-end devices should use external synchronization. That is, the synchronization of the image signals of each channel is controlled by the same synchronization signal. Causes the monitor screen to show sync.

Second, when using the LCD monitor to observe the image, why sometimes there is image distortion, distortion, inconsistent line and field, or even failure of the input signal?

1. The industry standard for LCD monitors stipulates that the input signal amplitude of professional LCD monitors is 1Vp-P±3dB (about 0.7Vp-P-1.4Vp-p) and the input impedance is 75 ohms. Therefore, if the input signal is not standardized due to cable attenuation, impedance mismatch, or the BNC head of the transmission cable, the input signal amplitude is much lower than 0.7 pp; either the camera output is not regulated or some irregularity is connected. When the input signal (such as distributor, amplifier, etc.) causes the input signal amplitude to be much larger than 1.4Vp-p, it may cause image distortion, line and field synchronization, etc.

2. Due to the wide video frequency range, the video signal is more susceptible to interference (including 50Hz power interference, electromagnetic interference, etc.) in the transmission process, thus affecting the image quality. Severe disturbances may cause images to be distorted, deformed, raceways, and lines and fields to be out of sync. Therefore, during the installation of the monitoring system, the video line must be far away from sources of electromagnetic interference.

3. The potential difference between the front-end device, the control host device and the terminal device may also interfere with the video signal, causing image signal distortion or image appearance of a race track if the whole system is powered on (ie, the front-end device, the master When the equipment and terminal equipment are connected to the BNC head to connect the front and rear equipment when they are powered on, it may be caused by the potential difference between the ground wire of the front and rear equipment (actually the shielding layer of the transmission cable). Fire, this severe flash fire will destroy the components at the input end or the leveling line in the PCB board casserole. Causes the input to open circuit and input no image fault. Therefore, the construction of monitoring system engineering should be designed and constructed in strict accordance with the specifications. The grounding bus should use copper conductors with sufficient cross-sectional area to ensure that the ground-to-ground resistance of the front and rear ends is 1Ω. The grounding line must not form a closed loop, and must not be short-circuited or mixed with the strong grid neutral line.

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