Five maintenance methods of the most popular color

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Five maintenance methods of color TV line scanning circuit

this paper introduces five inspection and judgment methods of line scanning fault, which can be combined flexibly and faster Find the fault location more accurately

I: line excitation 3.2 microcomputer should be used for special purpose. Due to the functions of the microcomputer itself, there are many methods to measure the emitter junction voltage and collector DC voltage of the tube and line output tube

by measuring the collector voltage of the line output tube, the chief accountant can judge whether there is a DC short circuit in the line output stage, but it is not certain that there is an open circuit fault in the output stage

by measuring the emitter voltage of the row output tube, the circuit with the fault at or before the row output stage can be judged The voltage of this emitter junction is usually positive or negative bias within + (-) 0.25V, which is related to the excitation mode of the row push transformer If the transmitting junction voltage is normal, it means that the line output stage was basically normal before; If there is no voltage at the emitter, it indicates that the impulse is provided at the end of the row driving stage or the row tube emission junction is broken down

when the row excitation tube works normally, the emission junction bias voltage is 0.4V The normal bias voltage indicates that the line oscillation circuit outputs normal line frequency pulses; The bias voltage is too small or no bias voltage indicates that the line oscillation circuit works abnormally or the line excitation tube breaks down; If the bias voltage exceeds 0.75V, the excitation tube will be saturated and turned on, and the collector voltage will be 0V, which is also the abnormal operation of the line oscillation circuit

II: row push transformer primary short-circuit method

if the voltage of the collector junction of the row output tube is significantly lower than the normal value, it can be judged whether the row output group is in DC short-circuit or AC Short-Circuit by pushing the primary winding of the transformer through the short-circuit row. After the short-circuit, there is no input pulse at the base of the row tube, and the row tube does not work in the pulse state Therefore, if the collector voltage of the row tube returns to normal after the short circuit, it indicates that there is an AC short circuit in the row output stage. The common faults are local short circuit of the row deflection coil, internal turn to turn short circuit of the row output transformer or its load short circuit If the collector voltage of the line tube is still low after the short circuit, it indicates that there is a DC short circuit in the line output. The common faults are the leakage between the CE poles of the line tube, the poor damping diode or the leakage of the reverse capacitor

please note that this method is not applicable to some color TVs For example, color 2 with frequency locked switching power supply High performance silicone and monomer: silicone is resistant to high temperature and high insulation, and the switching power supply is desynchronized by reverse pulse When the line circuit is not working, the output voltage of the switching power supply will drop If you lack experience in this field, you will mistakenly believe that there is a DC short circuit in the row output stage For another example, the main output voltage of some self-excited switching power supplies, such as Sanyo 83P and Fuji f91pptda, will rise to 143v and 130v due to load reduction when the line output stage is not working, which may cause undue faults

III: line push tube base signal injection method

when the protection circuit acts immediately after power on and it is difficult to judge whether the line frequency is low or whether the capacity of the reverse capacitance is reduced, the line protection circuit of the color TV can be disconnected, and a 0.5A fuse can be connected to the collector of the line tube at the same time; Then find a normal black-and-white TV, connect the ground of the two TVs with wires, weld the base of the push tube of the two TVs, and connect the line frequency pulse transmitted to the base of the push tube of the black TV to the base of the push tube of the color TV; If the color TV adopts a hot base plate, an isolation transformer must be used to supply power to the color TV When both TVs are powered on, if the color TV has a normal grating, it indicates that the fault is caused by the low line frequency; If the fuse of the collector of the color TV tube blows out quickly, the fault is likely caused by the reduction of the reverse capacitance

IV: secondary voltage measurement method of line output transformer

the high, medium and low electricity required by the TV set generated by the secondary of line output transformer, such as the 12V voltage of the verification regulation channel of "electronic universal testing machine" and "nonmetallic tension, pressure and universal testing machine", the 180V voltage of visual amplifier, and the 25V or 50V voltage of field scanning By measuring these voltages, we can judge whether the line scanning circuit is normal or not As long as the secondary voltage of one circuit is normal, it can be judged that the line scanning circuit is normal; If the circuits at all levels are abnormal, there must be a fault in the line scanning circuit

V: collector AC DB voltage measurement method of row push tube and row output tube

this is a very effective maintenance method The AC DB voltage of the collector of the color TV tube reflects the reverse peak voltage, and the specific value is related to the screen size of the model For 21 inch or smaller TVs, this value is 350-450 rounds

the approximate location of the fault can also be determined by measuring the AC DB voltage of the collector of the tube When the line management is not working, the DB voltage is zero; When the output load of the row output transformer is short circuited, the DB voltage is very small; If the DB voltage is normal but there is no grating or grating abnormality, it indicates that the secondary winding of the line output transformer is open circuit or negative, and the production of coal-based clean energy, high value-added fine chemicals and new materials based on this is loaded with faults; If the voltage exceeds 500V and the grating becomes small and bright, the reverse capacitance decreases

The AC DB voltage of the collector of the row pushing tube reflects whether the row pushing stage works normally The DB voltage is usually 75~125v, but if the row driving stage is powered by 24V low voltage, the DB voltage is within 50V

if the above methods are applied in practice, plus the specific analysis of specific problems, I think the general scanning problem can be solved

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