PCB Technical - Editor of pcb factory: Maintenance of high-pressure ignition failure of picture tube

Editor of PCB factory: Maintenance of high-pressure ignition failure of picture tube

The high-pressure ignition failure of the picture tube is also one of the most common problems in monitor maintenance.

It is mainly manifested by the appearance of many irregular bright spots on the phosphor screen grating, dotted lines in severe cases, and sometimes "creaking" inside the machine can be heard. If the fire is severe, the image will be blurred, and it may be in a few seconds or minutes. Then the grating disappeared. There are many reasons and parts for high-pressure ignition of the tube, mainly: high-pressure ignition in the tube holder; ignition of the high-pressure nozzle or high-pressure cap of the tube; ignition of the high-voltage lead end of the high-voltage package; poor internal contact of the focusing potentiometer and ignition, etc. . Let's talk about its maintenance methods separately below.

1. Maintenance of the CRT holder sparking
The ignition of the picture tube holder is generally at the focusing pole. The main reason for the internal ignition of the picture tube socket is that the environment in which the display is used is too humid or has not been used for a long time. Since the voltage of the focusing electrode is very high between 4KV and 9KV, the repair method is to turn off the power, remove the tube socket from the tail plate, scrape off the rust on the tube feet with a knife or fine sandpaper, and then use pure alcohol Clean it, and clean the rust on the plastic inner wall of the pipe seat with alcohol, then dry it with a blower, and then reinstall it.

2. Fire around the high-pressure nozzle or high-pressure cap of the picture tube
Fire is around the high-pressure nozzle of the picture tube. In addition to the humid environment, there is also inadequate contact or impurities between the high-pressure nozzle of the picture tube and the cone glass. To repair the high-pressure nozzle, you must first discharge it. The method is to flatten the knife with the large wooden handle, insert it into the high-pressure nozzle and touch the bottom plate several times. Sometimes you can hear the "popping" discharge sound. Then remove the high-pressure cap, check the high-pressure nozzle and the high-pressure circlip for rust, and whether there are signs of ignition and dust accumulation around them. If so, you can clean it up according to the previous method, and then use a hair dryer to dry it. Pay attention to the temperature and time to prevent the display tube from overheating and bursting. Then spread some butter evenly around the high-pressure nozzle, and then buckle the high-pressure cap.

3. Ignite the high-voltage package and the focus potentiometer
The ignition of the high-voltage package can cause the grating to be blurred or no grating. If the ignition coil itself is ignited, then it has to be replaced with a new one. If the lead end of the high-voltage package ignites, you can wipe it clean with pure alcohol and drip a little insulating varnish. If the focus potentiometer on the high-voltage package is ignited, you can adjust the focus potentiometer several times after shutting down to see if it can make the internal contact contact better. If not, replace it.

How to degauss the display
It is also a common problem that the display screen is magnetized and appears colored spots. The main reasons are: the display is magnetized near the magnetic object; after moving the display, the deflection coil in the machine is shifted, resulting in poor color purity; the degaussing circuit is damaged. Although some displays have a certain degaussing function, they are somewhat powerless for severe magnetization.

For poor color purity caused by interference from external magnetic fields, an external degausser can be used to degauss. Degaussers can be purchased or self-made. In case of emergency, you can find a used watt-hour meter (1A～5A can be used), remove the voltage coil, and remove its "gate"-shaped core, leaving only the T-shaped iron core and the coil penetrating the coil, And then connect the power cord and switch plug to the two terminals of the coil, and then wrap them with a plastic cloth. But no matter what kind of degaussing method, we must pay attention to safety. After power-on, hold the degausser and keep shaking, gradually approaching the phosphor screen, and repeat the operation on the magnetized parts. Then, while shaking the degausser, move back to about 2 meters away from the phosphor screen and then turn off the power. The power-on time should not be too long each time. If the degaussing effect is not good, it can be repeated several times.

Due to the poor color purity caused by moving the display, you can open the back cover of the display to restore the deflection coil to its original position, and tighten the deflection coil screw. For poor color purity caused by damage to the degaussing circuit in the machine, first check whether the thermal degaussing resistor is damaged, take it off, and shake it by hand if it makes a "swooshing" sound, it means the thermistor is broken. Use a multimeter to check the resistance of the pins. If the resistance is less than 8 ohms or greater than 50 ohms, it indicates that the RTC component in the degaussing resistor is broken and should be replaced. If the resistance value of the degaussing resistance is normal, check the leads of the degaussing coil, plugs and sockets for looseness and poor contact.

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