Based on past experience in maintenance: la7830 fault rate is relatively high, field amplitude increases fault with only feedback element and its related, and little relationship with other peripheral parts. Check C823R829 no abnormal replaced directly after la7830, but constant failure. Analysis may TDA8375A output of field sawtooth wave amplitude is not normal. Check the relevant drawings, TDA8375A46 pin for the field feedback input, 47 feet for the field of the reference voltage of the field, 51 pin voltage (3V) when the image is pulled up, 52 feet for the field of the wave of the base. When measuring a 51 pin voltage (3V) image to pull the measured 51 feet (4V) voltage image character pulled longlier, view field amplitude increases with the feet voltage related to abnormal. The C332, R321 (39K) detection is normal, and the TDA8375A circuit is deduced. Because the TDA8375A price expensive and difficult to purchase, decided to make the circuit components on 51 feet, 52 feet outside the appropriate changes. Namely take down R321, in the R321 position welding a 100 K adjustable resistance, after adjustment, the image is restored to normal. Because r321 is a chip resistor, adjustable resistance welding in the above is very convenient, decided to take it to measure resistance, and resistance welding in the r321. Take adjustable resistance measurement was surprised to discover that: can the resistance value of the adjustable resistor and the original r321 (39 K) of the same, with a 39 K resistance welding at the r321, image restoration of normal.

Summary of the maintenance and get a hint: (1) normal resistance measurement, not working properly; (2) resistance when a fault occurs, not only adverse or increases the resistance of the fault contact and resistance decreases possible (in this case, the resistance decreases); (3) corresponding with TDA8375 (tda8366) small signal processing Sony G series of color TV, adjust the resistance of the 52 foot r321 can change the amplitude of the size.