أعطال الجهد العالي .. كتاب التلفزيون الملون والعادي

17-20 High Voltage Faults:

Most of the faults in the horizontal deflection stage in the monochromatic and colored devices may be caused by the high voltage section or from a defect in one of the elements of this section - and let us not forget that the absence of high voltage may also result from other circuits in the horizontal deviation stage. If for some reason the deflection wave does not reach the output transformer, the high voltage is not generated at all.

The valve high-voltage rectifier is responsible for high-voltage malfunctions. Therefore, devices with transistor elements and solid resistors are more reliable and effective. The presence of coronal branching weakens the high voltage as well. And in colored devices that contain circuits for regulation, the possibility of malfunctions of the elements of regulation is added. As the failure of the regulating circuit, or the high voltage rectifier, or the horizontal output transformer, as well as the failure to adjust the high voltage controls, all lead to preventing the generation of high voltage or weakening it a lot or increasing it, so the image does not appear or becomes dull. In addition, the focus circuits in color devices may malfunction, especially since the focus coils deal with high voltage pulses as well.

A - Bypassing the return current:

Some of the faults in the horizontal circuits may cause an increase in the strength of the return current passing through the horizontal output circuit, so the temperature of the insulating materials rises and leads to their failure - and the discharge and the occurrence of sparks heat some areas and melt the wax insulator and cause various malfunctions - and the presence of molten wax spots at the bottom of the high voltage cage This indicates that there is a defect, and the examination must be carried out to find out the cause, then the reset is done to reduce the current passing through the recoil transformer before the failure worsens. The picture shows Figure (32-17) the presence of a short circuit in the deflection coils.

B - adjusting the horizontal centering:

The adjustment of the horizontal centering includes the skew current - if the adjusting element is of the carbon type, it is subject to wear and tear. This leads to a loss of adjustment or adjustment at one end, and in both cases the image becomes shifted to the left or right.

The relationship between horizontal circuit faults and high voltage:

Correct high voltage generation is related to the safety of the horizontal stage operation. Any defect in the horizontal output transistor will disable the power supply to the flyback transformer as well as to the deflection coils, so that no high voltage is generated, and no lighting appears on the screen.

A - Flyback transducer malfunctions:

If a cut occurs in the primary (lower) windings of the recoil transformer, the current will pass
+ B to the output transistor or LED will turn off. Thus, high voltage is not generated. As for the occurrence of a short circuit in the transformer, it will often appear with smoke and smell. As a result of the high temperature of the short point, the generation of high voltage is also disrupted. A cut may occur in the high-voltage coils, and the high-voltage stops. As for the occurrence of a short circuit in the high-voltage coils - even one turn - this will affect the performance of the entire recoil transformer - the short circuits absorb some power and greatly reduce the high voltage.

B - Malfunctions of the damper circuit:

This is for valve devices only which includes the horizontal output valve which requires a high voltage +B + for this valve to operate in Class C. Any defect in the booster filter reduces the voltage to a lower value than required. Thus, the power delivered to the recoil transformer and the deflection coils is not enough - and the little power returns to the circuit during the recoil period, and the high voltage generated will be incorrect.
The damper charges the booster filter and the occurrence of a defect causes the high voltage to be completely lost, or weakened and reduced.

C - Malfunctions of deviation files:

Deflection coils are connected to the return transformer. Compatibility must be checked. Opening the deflection coils circuit leads to loss of voltage (B). The occurrence of a short circuit in the deflection coils is indicated by the high voltage drop and horizontal distortion as in the previous figure. So make sure that the supply voltage of device + B is of sufficient value. It does not contain very large zigzags.

Corona discharge faults and sparks:

Sparks are generated in adjacent elements of high-voltage circuits - a corona discharge is like a thin electric arc. It occurs in the air or with nearby grounded parts. The presence of protrusions, letters and sharp heads is the most appropriate place for the emergence of these sparks and coronal branching, and the occurrence of sparks may be accompanied by a rustling sound (hiss) or popping. The sound may be weak and difficult to hear, and the best way to detect the location of the discharge is to place the device and operate it in a completely dark place, then monitor and inspect the location of the sparks and the discharge point. Spark discharge is not harmful in and of itself, but its side effects. Harmful, especially in the high-voltage transformer and in other circuits. Sparks make the air ionize, so it becomes a conductor, and the sparks are accompanied by high heat, which may burn the insulator, char it and pierce it sometimes, and damage the connection points of the circuits adjacent to the sparks. the job.

The accumulation of dust particles and others in the high-voltage cage or around the screen fasting elevator - increases the possibility of branching and arches - and cleaning the high-voltage places reduces the possibility of branching. The high voltage, the voltage multiplier circuit (Cascad) and the transistor or the horizontal output valve are also manufactured in a manner that bears the high voltage and does not have protrusions or sharp edges that help in issuing sparks - Figure (33-17) - in addition to that the high voltage areas are surrounded by a metal cage to isolate from the elements and neighboring circuits and protect them from leakage of sparks to them.