Color display power supply characteristics and maintenance - Power Circuit - Circuit Diagram

2) The filament voltage of the color TV is generally provided by the line output transformer (AC), and the filament voltage of the color display is directly provided by the switching power supply (DC 6.3V). Color display adopts this power supply method, mainly to meet its energy-saving requirements, that is, when the computer has been unattended for a period of time, the color display enters the energy-saving state. At this time, the field scanning stops working, and the whole machine consumes a large amount of power. Drops, and the filament is normally heated, and once someone operates the computer color display, it immediately enters the working state.
3) The output level power supply of the color TV is generally about 110V and fixed, while the color output line output stage power supply is mostly between 45V and 135V, which is usually not a fixed value. The reason for this difference is that the scanning frequency of the color TV is fixed, and the current SVGA color display has multiple scanning modes. The scanning frequency of different scanning modes is very correlated (the line frequency range of color display below 15 inches is 30~54KHz, and the range of line frequency of large screen color display is larger). In order to ensure normal line scan amplitude and reverse pulse amplitude (appropriate high voltage) in different scan modes, the line power voltage of the color display in different modes also varies with the line scan frequency, and the line frequency is higher when the line frequency is higher. The voltage is also high. The common switching power supply is a fixed output, and then the secondary switch regulates the output. The fixed output is 45V and 150V, 45V is double-regulated to obtain 45V`~135V for the raw pressure type; 150V is secondly regulated to obtain 45V-135V for the step-down type.
Due to the power supply circuit, the fault phenomenon is mainly no grating or grating abnormality.
1) The first step of maintenance is to observe the power indicator light, whether the light of the picture tube filament is normal or not to judge whether the switching power supply works normally or not. If it is not normal, the switch power supply itself has a problem or the load has a short circuit; if the light is normal, it is necessary to continue to detect the output voltage of each group of the switching power supply. It is judged whether the switching power supply works normally, mainly based on whether the output voltage of 12V is accurate. If 12V is normal, the switching power supply itself is generally no problem.
2) In the case of normal switching power supply, there are several possibilities for no grating fault: the first one is the line scan circuit or the picture tube circuit fault, which is the same as the color TV; the second is the secondary switching power supply abnormality, check the line output The power supply voltage of the transformer can be determined; the third is a fault in the energy-saving circuit or the pattern recognition circuit, which may cause the secondary switching power supply to not work. It should be noted that some color displays must be connected to the host before they can be started. In the offline state, the energy-saving circuit will automatically turn off the line scan because there is no synchronization signal.
3) The grating anomaly is mainly because the width is too large or too small, and the width adjustment knob on the adjustment panel cannot be adjusted to the normal amplitude. This type of fault is mostly caused by abnormal line voltage, fault in the line pulse amplitude sampling circuit or line power secondary buck circuit. In addition, the line amplitude abnormality occurs in the circuit of the reverse circuit capacitor and the S-circuit positive capacitance automatic adjustment circuit, and the maintenance method of the field amplitude abnormality is the same as that of the color TV.