The LCD screen is blurry. What's going on?

Blurry screen display is one of the common faults of various monitors. There are three main reasons for its occurrence: First, the focus potentiometer of the FBT (line output transformer) is loosened due to vibration during transportation or use. Or it shifts, causing the focus voltage added to the CRT to change (deviating from the optimal voltage value debugged at the factory), causing the screen to be blurred; second, the use environment has high humidity, causing the discharge ring (semi-circle) of the focus pin on the CRT tailstock board to ball) produces rust, and blurring occurs when the CRT is first powered on; third, due to the manufacturing process in the CRT tube or debris in the CRT cone glass envelope, electrostatic dust is generated between the focus pole and the accelerating pole (G2). It forms extreme resistance and causes severe blurring on the screen. How to determine the cause of screen blur? First of all, from the perspective of the degree of screen blur, if the blur is mild and only the character outline becomes thicker, but the handwriting can still be recognized, it is mostly caused by the first reason; if the characters are severely blurred in a large area and the screen is covered with a white halo, If the characters are unrecognizable and the screen brightness changes when adjusting the focus potentiometer on the FBT, it is the third reason; if the CRT is blurry when it is first turned on, the characters on the screen will become clearer and clearer as time goes by, which is usually the case. Caused by the second reason. Now that you have figured out the cause of the blurry screen, how can you troubleshoot based on the fault symptoms? For the first case, open the cover and fine-tune the focus potentiometer in the FBT to eliminate the fault. As for the corrosion treatment of the discharge ring of the focusing pin on the tail plate, anhydrous alcohol is generally used to clean the discharge ring and the electrode plugs and sockets on the tailstock. If the discharge ring is severely corroded, the tailstock parts can be replaced. The method to deal with the blurred screen caused by the third reason is: remove the CRT tailstock plate, and lead the 24KV high-voltage multimeter lead wire from the high-voltage cap on the CRT (it is best to use a digital multimeter with better insulation performance) to the CRT focus plate socket. , turn on the AC power supply of the monitor, use a grounded test lead to instantly discharge the accelerating pole (G2) plug 2 to 3 times (it is best to use an external protective sleeve to lead out the G2 plug on the CRT, and ground the lead wire for an instant discharge operation). Generally, after 2 to 3 discharge processes, the dust electrode resistance between the focus and accelerating electrodes (G2) can be broken down. After restoring the original circuit, observe the clarity of the characters or graphics displayed on the screen. If necessary, adjust the focus potentiometer on the FBT appropriately to eliminate the blur fault. This method is often called the "Acking method". Because high voltage is involved in the operation, you should be cautious and remember to protect the safety of people and equipment. It should be noted that the above-mentioned screen display blur fault does not include those screen disorders caused by improper adjustment of the accelerating pole (G2) voltage, inappropriate adjustment positions of the brightness and contrast potentiometers, etc. It seems to have a hazy feeling. situation included. For monitors such as IBM 2248/G03, Envision/D350, etc., use a rubber hammer to aim at the center of the CRT screen and gently hit it several times. There is a 50% chance that the blur fault of this type of monitor can be eliminated. This can be regarded as a shortcut to repair the blur fault of the monitor. .