Grating brightness change along vertical direction, the fault is consistent with the field scan cycle. Therefore, doubt in video signal with the field scanning signal or blanking is not normal. Because the machine has been used for years, the first suspect machine maintenance switch leakage is installed inside, make field scanning circuit signal transmission by the maintenance switch to see. To repair the connection to the switch to cut off the field scan, fault is still. Turn the field blanking circuit. As shown in figure 5, the machine of blanking by line, field oscillating circuit IC701 output (LA7801) pet-name ruby foot, after R606, D601, and the line from D782 flyback pulse blend into the decoding circuit IC50118 feet, under the effect of internal circuit implementation, and field scanning during blanking blanking. U63service manual download site
 U63service manual download site
Try to disconnect R606, the original fault phenomenon disappear, but the upper part of the screen flyback lines, determine the fault is present blanking circuits. Doubt D601 damage, measured with the oscilloscope IC701 pet-name ruby foot voltage waveform as shown in figure 6 a, here the correct waveform should be as shown in figure 6 b. Obviously, after the deformation after the blanking is present during the flyback cannot quickly down to a low level, cause field are beginning part of the electron beam is still closed, so that form this case fault phenomenon. U63service manual download site
 U63service manual download site
After blanking after deformation along with capacitive discharge curve of the same formation, thus suspected IC701 pet-name ruby foot external capacitance C601 capacity increases, but remove the C601 measurement, capacity is correct. Don't answer C601 of commissioning, they found fault disappear, see IC701 pet-name ruby feet signal waveform distortion will be no more, will remove the C601 of fault appears again after back, but after the replacement of C601 fault, still there are other faults in the circuit. According to the analysis of pulse waveform after deformation, increase of C601 discharge loop time constant, thus suspected R787 resistance value increases or open circuit, remove the check has been open, replaced and troubleshooting.

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