1, check whether the picture tube is aging. For general maintenance personnel, due to the lack of special instruments and equipment, it can only be done indirectly. The specific method is as follows:
Turn the brightness potentiometer of the picture tube to the maximum, power up the display and observe the grating. If the grating appears for a long time and the brightness is insufficient, it means that the picture tube is aging. If the grating appears at a normal time (compared with the normal display), the picture tube is not aging. Sometimes, slight air leakage or sparks between the electrodes of a picture tube can also lead to poor focusing. For the inspection of kinescope air leakage, you can observe the neck of kinescope. When the neck of the picture tube is filled with fog, it means that the picture tube is leaking. Check whether there is a spark between the electrodes of the picture tube, and you can directly observe the display of the fluorescent screen. If the displayed content is vague but stable, there will be no spark between the electrodes of the picture tube. The inspection showed that the picture tube was not damaged.
2. Anode high voltage can be directly measured by high voltage meter. Never use a multimeter to directly measure anode high voltage without a high voltage meter. Commonly used methods are:
(1) When the monitor is powered on, pay attention to whether the deflection coil has obvious high-voltage charging sound. If so, high voltage is not a big problem; If not, it means that there is no high voltage or insufficient high voltage on the display.
(2) After the monitor is powered on, gently touch the screen with your hand to see if there is electrostatic discharge sound. If so, the voltage is basically normal; If there is no or the electrostatic discharge is not obvious, it means that there is no high voltage or insufficient high voltage on the display. After inspection, the anode voltage of CRT is basically normal.
3. Check the focus voltage. Adjust the focus potentiometer of CRT (on-line output transformer), and the display content is as clear as before. After less than half a day of use, the fault phenomenon reappeared. After inspection, it is found that the knob of the focus potentiometer is fixed with silicone rubber, which is very elastic. After the initial adjustment of the potentiometer, it was not fixed again. After a period of time, due to the elasticity, the silicone rubber pulled the potentiometer back to its original position, so the fault phenomenon appeared again. Adjust the potentiometer again and fix it with epoxy resin, and the fault is completely eliminated.