Field scanning circuit schematic , ( 31 ) # field sync pulse signal output from the signal pre- processing circuit smaller TA8719, followed by finishing to add ② # LA7838 sawtooth formation of the field pulse signal and performs power amplification , the amplified field pulse signal from the ( 12 ) # output in place by the sampling resistor R459, C458 , etc. to form AC and DC negative feedback to complete the pre- field amplitude sawtooth wave forming circuit adjustment , R463 for the field amplitude potentiometer , +30 V, VD451, C455 constitute power supply circuits. During the reverse process is completed field scanning dual power supply .
Failure Analysis and Maintenance : TV now a bright horizontal line, which is a fault -field scanning circuit common , we should follow the maintenance steps to overhaul detours .
Step one: look at the brightness maintenance switch is in the maintenance position , check the field of external components , the deflection and terminal, the output coupling capacitors.
Step two : check -field amplifier, power amplifier , a current limiting resistor , bootstrap components , amplifier block itself .
Third step: check the small signal pre- processing , using an oscilloscope to see if there is a pulse output , if a fault in the output stage , before the investigation is now no output power stage IC , oscillator timing components , and field oscillation block itself and so on.
For this circuit deflection coil leads us first to check the plug, the output coupling capacitor , this capacitor is damaged, pin mildew can cause an open circuit failure, measuring the deflection coil resistance is normal. Power , power measurement amplifier block # 6 is 0V, the power to check the positive and negative phase diode VD451 resistance is normal, there is no 26V amplifier power forward Charles , and then forward the investigation, before the 26V power supply inductance normal , power supply testing inductance is open , replace the power inductor is energized and burned, measured field amplifier manifold ( 6 ) # on the ground only a dozen ohms resistance , doubt has been damaged, replace the manifold LA78041 field and then for inductive amplifier circuit back to normal.

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