This symptom is not synchronized and no sound, Auto search does not exist, the slant pattern searching signal screen is cluttered, the image isn't going to suddenly flashes, continuous on/off machine. Original storage bench can appear normal, and excellent in sound. Sometimes when you change the channel correctly, sometimes fail.

According to symptoms, similar to a don't-detuned, and after dismantling machine powered on. Measure the N301 (TDA8844) (12) 8V and feet (37) pin 5V supply voltage are normal and stable. Then check (5) foot R301, C303 PLL circuit in the image without exception, based on past experience, and (5) foot of two components with exception, sometimes absent figure or pale, sometimes cause instability in the PLL circuit is not working properly and the image. For safety's sake, after substitution C303 still invalid. Failure for other reasons. Thus, further testing (53) and (54) feet of the AGC voltage, 2-4V changes the voltage value, suggesting that. AGC control properly. Reference related data analysis, (42), (43) foot external components are PH1-1, PH1-2 filters, filter elements, please refer to the internal circuit. Analysts believe that the fault should be (42), (43) filter elements outside of the foot is directly related, if the external components is no exception. Only doubt TDA8843 internal damage. According to Jane prior to propagation, detection routine in the outside first and then, carefully check (42), (43) foot external filtering components. C409 measured results by MF-47 multimeter (1 μg F/50V) tantalum capacitor is no exception, set the meter to be measured in Rx10k block, measure some leakage around 420k ω resistor, after replacing it. All the fault elimination, everything is back to normal.

Faults are excluded. But why always perplexed. As usual. Frequency offset or synchronously should not affect the sound and automatic search, this fault comes to, in case of failure, along with the audio disappears and automatic search does not exist. In order to explore reasons, the author of TDA8844 internal and external circuit for further analysis and study, originally TDA8844 circuits are used at the time of application. (55) outside the foot into an increased capacitance. When identifying the circuit when no video signal is confirmed. To add port will automatically mute where to add the equivalent of video detection automatic mute function. The other hand, the Sandcastle pulse is normal, return pulse according to a certain pattern by combination of composite sync pulse, which due to (43) PH1-1 bad filter capacitor leakage outside the foot. Oscillation Frequency Oscillator start from row row raises an exception. This will inevitably lead to the sand Castle Sandcastle pulse generator produces abnormal pulse. Sandcastle synchronized pulses is determined by the color strobe, row, field blanking pulse composed of composite sync pulse. The pulse is normal or not, related to image scanning correctly, clamping, row, field blanking brightness, delay in synchronized color separation, color, clamp the base color, graphics and text-processing functions such as demodulation circuit, it is not difficult to find. It is the Sandcastle pulse vibration frequency of exceptions and exceptions are produced. So just leads to various complications appear. Including effects to the sound, and Auto search does not exist.

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