أعطال دارة تغذية الجهد المنخفض .. كتاب التلفزيون الملون والعادي

16 - 12 Malfunctions of the low voltage supply circuit:

DC power supply circuits have only three types of faults:

1- All continuous efforts are completely lost.

2- Decrease in one or more efforts.

3 - AC zigzags on one or more continuous voltages.

* 1 - Loss of all DC voltages:

When there is no DC voltage - it will not show a picture or sound, and the reason for this malfunction is as follows:

1- Melting of the voltage fuse B or the main fuse.

2 - Short filter capacitor.

3 - Malfunction in the rectifier circuit or the diodes.

4- Separation or cutting in a file or filter resistance

E - Separation in the protection resistance.

The box diagram (12-21) shows the follow-up of this malfunction.

One DC voltage loss:

The appearance of the malfunction will be proportional to the lost effort function and the circuit that feeds it. These are some of the reasons for this holiday.

1 - Open in the filter resistance

2- An opening in a binding resistance.

3- A short circuit in a pass capacitor.

* 3- A drop in DC voltages:

The decrease of all continuous voltages can cause the image dimensions to be reduced horizontally and vertically. The lack of a linear structure of the image (raster) can cause poor lighting - in which case the focus will be weak - and some of the reasons for this malfunction are:

1- A decrease in the AC network voltage (when the regulation circuit is working properly, the effect of the decrease in the network voltage is weak or non-existent).

2- A defect in regulating the supply voltage.

3- An opening in the feed inlet filter capacitor or a decrease in its capacity.

4 - Malfunction in the calendar diodes.

E - a significant increase in the load as a result of a malfunction in one of the components of the device.

Zigzag feed source:

The zigzags of the feeding source are due to the leakage of the AC zigzags of the DC feeding source, and this is what basically happens. Poor filtering or opening in the filter capacitor. Also, increasing the impedance of the feeding source can cause communication between some circuits and generate low-frequency oscillations. An opening in one of the rectifier diodes in the rectifier bridge circuit leads to the conversion of the rectification from a full wave to a half-wave, i.e. from (100) Hz zigzags to 50 Hz, and the effect of these zigzags increases when there is a defect in the regulation circuit. In its proper condition, the filtering and filtering of the current is improved. The image shows successive horizontal black and white lines with a frequency of (50) to 100 Hz. At a frequency of 50 Hz, there will be one wide black and white line, and at a frequency of 100 Hz, there will be two lines for each. And if the zigzags break in the horizontal scanning circuit - the linear structure of the survey will withdraw horizontally - and each vertical side of the scanning structure will appear in the form of a sine wave of 50 Hz or two waves of 100 Hz. But if the zigzags are in the horizontal synchronization circuits, then withdrawal will appear in the image only. Not in the linear structure of the survey. The zigzags in the vertical synchronization circuits can cause a weakening of the vertical synchronization, and the zigzags may affect the sound, so it appears in the form of (they are) or a buzzing and flickering in the picture.

12-17 Malfunctions of the horizontal frequency feed:

​​​​​​There are some malfunctions that can occur due to the horizontal frequency feed: Returning to the previous feeding circuit diagram, we find that in the absence of a picture or sound, the probable cause is one of:

1 - 150 volt rectifier circuit

2 - Start circuit

3 - Horizontal regulator (110) volts

4- Horizontal circuits or horizontal output transformer.

If any malfunction occurs in these circuits and they do not work well, the derivative voltages B + will not be generated. The device does not work completely, and the voltage circuit (27) (volts) stops the work of the horizontal circuit and works when the derived voltages B+ increase to an unacceptable value. The overvoltage protection circuit will stop the work of the horizontal oscillator - so all derived efforts will be cut off, and the device circuits will stop working. And then the device must be turned off and then turned on again to return to work. If this malfunction continues, it requires cutting the current and starting the repair procedure
The reason for this malfunction is most likely to be an excess of the regulated output voltage (+110) volts, which causes a short circuit in the thyristor SCR or the filter capacitor, meaning that several efforts are generated from the secondary coil of the horizontal output transformer - and any defect in one of these efforts will be disrupted and disturbed in the circuit that Fueled by this effort has passed.