انبعات أشعة x في الأجهزة الملونة .. كتاب التلفزيون الملون والعادي

17-18 X-ray emissions in colored devices:

X-rays are harmful to the body and the eye - and are emitted when the amount of high voltage in the screen valve of the color device is exceeded - but it is certain that the rays emitted from any color device in the natural state do not have any effect on the viewer - even if a person is exposed to photographing his chest, body or jaw once One with a Roentgen X-ray that gives him more radiation than what he gets from a TV set in several years.

X-rays are emitted from the collision of the electronic beam with the screen or any object at high speed, and this voltage must be exceeded
(10-15 kV). But the presence of the glass cover of the screen makes the voltage generating X rays must be more than (20 kV) and the rays are measured in the unit of Roentgen R or milliRoentgen (MR), and the effect of the distance of the rays is inversely proportional to the square. (4) Millie (Henry) at a distance
(20 cm) The screen is equipped with materials that dampen the intensity of the x-ray, such as metal - glass - ceramic. The source of x-rays in color television is:

1- High voltage regulator valves and high voltage unifier in valve devices, which are no longer in use.

2 - Image screen valve. It is equipped with a circuit not to exceed the high voltage, especially the devices manufactured after the year /1973/

​​​​​​Some health organizations for some countries have determined the amount of x-rays in TV sets to be no more than (05 millihenries / hour). Within this limit, the device does not pose any danger or problem to humans. X-ray protection circuits or protection circuits Exceeding the high voltage: These circuits cut off or reduce the high voltage connected to the screen elevator when it exceeds the safety limit. The methods used for this are:
1- Changing the frequency of the horizontal or vertical oscillator so that the image is distorted. It is not watchable.

2- Preventing the image signal from reaching the screen valve.

3- Disrupting or stopping the horizontal circuits, which prevents the presence of high voltage.

4- Reducing the high voltage. This makes the screen dim and out of focus.

These solutions must remain in the device until the danger of exceeding the voltage ends, then the situation returns to normal. All of which aim to distance or prevent the viewer. Proximity to the device to protect it from the damage of X-rays emanating when exceeding the high voltage.
High voltage surge protection circuit and X-ray emission by changing the frequency of the horizontal oscillator:

This circuit is based on changing the frequency of the horizontal oscillator away from its regular frequency, when a high voltage is exceeded on the screen valve elevator, so the image becomes unacceptable to the viewer.

Circuit working principle:

This circuit (Fig. At normal high voltage - the CR9 diode pulses - and the resulting DC voltage is applied to transistor 0 which is PNP type, so it has a radiant bias (+22 F). As for its base, it is determined by the voltage (8, 22 V) using a CR11 zener diode. Thus, the radiated voltage is less positive than its base voltage during normal operation. As a result, 2 is in a cut-off state and does not spoil the oscillator's work.

As for when the high voltage rises beyond its limits, the amplitude of the applied horizontal pulse increases beyond its normal limit - so the positive emitter voltage of the Q7 transistor increases, and this is sufficient to make it in the connected state - and then it is connected through the binary (CR). It gives the wrong DC voltage in the AFC circuit - directing the horizontal oscillator away from its frequency. This continues until the defect is gone and the high voltage returns to its prescribed limit.