أعطال صمام الشاشة للأبيض والأسود والملون .. كتاب التلفزيون الملون والعادي

11-18 Malfunctions of the screen valve for black and white and color:

1- Lack of lighting:

The possible reason for this malfunction is:

A - A malfunction in the high voltage circuit that feeds the screen valve elevator and some of its poles.

B - A malfunction in the circuit of the network or the cathode of the valve, so the screen remains dark because the beam is in the state of cutting.

C - Burning or interruption in the heating wick of the valve, preventing the ray from radiating towards
Screen as a result of not heating the cathode.


The latter malfunction is classified as a costly and annoying one, because it requires changing the screen valve completely, and some attempts to re-weld the filament may succeed, as we will explain later. Fortunately, this malfunction rarely occurs in modern valves, due to the improvements that have been made to the heating filament to withstand greater voltage and current. .


Attempt to re-solder the cut filament:

This attempt is made as the only and final means before changing the screen, due to the exorbitant price of the screen valve or the lack of a replacement valve with the same original specifications, and this attempt is made by means of the high voltage of the device. as follows :

1 - Remove the screen valve base plate from its position on the screen poles.

2- The two ends of the filament feed shall be shortened to the base plate, if the device has other valves connected in series with the screen valve (in the old types the screen is close to the valve metal).

3- We connect one end of the filament to the metal of the device.

4- We gradually remove the end of the high voltage cable from the device after you turn on the device and when a violet spark appears, we gradually bring the high voltage cable closer to the ungrounded end of the filament, so a spark is generated between the two ends of the cut and you weld them if they are in a close position.

E - We turn off the device and make sure that fusion occurs by means of an altimeter (ohm field) between the two ends of the filament, and the previous process is repeated if fusion is not achieved until the connection is complete.

6- If the breakage is large, the welding process is not successful and must be replaced

2 - Poor lighting and contrast is not good and the method of loading the screen):
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If the appearance of the image is delayed after turning on the device - and the image is weak in contrast (often with a silvery appearance). This indicates that the screen valve has become gassy or there has been a weakness in the cathode emission - in this case the valve can be activated as follows:

1- Separate the feeding of the screen filament - and shorten the two feeding ends in the valve devices that have a sequential feed for the valves. In modern devices, we isolate the two feeding ends after separating it from the filament.

2- We feed the heating filament through an additional transformer whose primary end is (220) volts alternating and connected to the device’s operating switch. Its secondary voltage (6 - 7,5 - 9 volts) feeds both ends of the filament: we try the appropriate voltage, starting from 6 volts, until we see an improvement in the image. Figure (11 - This voltage, which is greater than its normal voltage, increases the temperature of the filament, and the activity of the cathode emission increases, and the image on the screen improves.
Note: This process does not guarantee the continuity of the screen and its functioning, as this period may be shorter or longer.

The filament of the weak screen valve can be fed as a result of the weak emission of the cathode due to the long time of its use) - via the high voltage transformer as follows: An insulated wire is wound on the magnetic circuit of the high voltage transformer for two turns or more and their ends are connected to the screen filament after performing the previously mentioned steps, especially separating the two ends of the original feed. about her. The number of rolls increases one roll after another, and we try and test the image quality until we reach the desired. Noting that increasing the windings increases the voltage and shortens the screen activation time, or damages it after a very short time.

3- Increasing the brightness of the screen and the inability to control or reduce the lighting:

This phenomenon often indicates a contact (short) in the network inside the screen valve. The following steps can be taken to remove this palace:

1- Turn on the device for a period of time to heat up the electronic ejector inside the screen.

2- We charge a chemical capacitor with a capacity of (100) (microfarads) (350-450 volts) by connecting it to both ends of the main filter capacitor of the device in the main rectification circuit.

3- We discharge the charge of the capacitor at both ends of the ruling grid and the cathode. Or between the first and second networks, depending on the location of the contact and the short circuit.

4- The attempt should be repeated several times if necessary until it is clear that the palace is gone
4 - Wide horizontal black lines in the image:

This phenomenon can occur in black-and-white or color TV and indicates the presence of contact between the filament and the cathode - and to address this situation in a cheap and easy way - an isolating and reducing transformer from 220 to 6-12 volts (400 milliamps) is used to feed the heating filament from it. The primary coils are fed with the television set at a point located after the operating switch - the current is connected to the device when the main circuit breaker is closed. Thus, the cathode circuit is isolated from the filament circuit - and the black screen lines affected by the feeding frequency (50 Hz) disappear - and leakage from the heating filament to the cathode.

E - large color spots that cannot be controlled:
It arises from the magnetization of the image diode, which causes the rays to diverge outside its target, and this results in the magnetization of the screen - and this color smudge is removed by using an external demagnetization file, in the manner described in the demagnetization method, and since modern devices are equipped with a demagnetization file - it surrounds the back wall of the screen and works automatically - When the device is turned on, which in most cases obviates the use of an external file. It is sufficient to operate the device once or several times, provided that we leave a sufficient time after turning off the device and before restarting it. Some companies recommend leaving a time of 20 minutes before turning it on again.

6- Only two colors appear and the third color disappears:
This indicates a malfunction in one of the launchers. It is the ejector that gives the hidden color, and the fault may be in one of the circuits related to this color - or the loss or weakness of the voltage feeding its circuit.

7- Weakness in one of the three colors: This is a weakness in the emission of the cathode of one of the launchers or in a circuit belonging to it.