According to the grating very dark phenomenon, first detected three video outputs amplified manifold IC351 and peripheral circuits , measuring 2,3 feet IC351 video signal input voltages are 1.8V, 5 feet ( non-inverting input ) , 6 feet ( video level 221V supply voltage terminal ) voltage is also normal , but 7,8,9 foot (B, G, R output terminal ) voltage are about 205V, ( normal is about 150V), visible due 7,8 , 9 feet high voltage caused raster dark. Charles IC351 peripheral components without damage , each measuring IC351 feet on the ground , the reverse resistance value normal estimated IC351 not damaged , IC351 is not in the normal enlarged working condition, but in the off state.rQpservice manual download site
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    Along the B, G, R to check the input signal forward , 12,14,16 respectively IC3401 pin voltage 1.9V, 2.0V, 1.8V, the normal 3.6V, 3.5V, 3.6V; 6,3,1 pin voltages are 1.7V, 1.7V, 1.6V, normal is 3.5V, 3.4V, 3.5V; while the 5 foot 12V power supply is normal. Power supply input pin 19,36,50,59 etc. then check IC601 , and are about 7.6V, while the normal should be regulated 9V power supply. D along the circuit board to board inspection , found three-terminal regulator block IC805 D board 3 -pin output voltage of 7.6V, 1 pin input voltage is only 8V, but the voltage across the normal C836 12V, description R842 pressure drop is too large. Remove the check R842 , R842 has changed is about 4.7Ω 14Ω. After using 4.7Ω / 5 people resistor replacement, troubleshooting .rQpservice manual download site

    Since the R842 resistance increases , so IC601 supply voltage drop from the normal 9V is about 7.6V, and IC601 both video processing , multi-standard chroma decoding , horizontal and vertical sync separation , scanning oscillation excitation functions , causing R, G, B video signal output becomes small , resulting in R, G, B amplification bias changing circuit , the three CRT cathode voltage applied signal becomes high , the basic beam is turned off, so the grating is dimmed. Simultaneously oscillating field is not normal , so to see a dark shadow flicker , swing around and there is the phenomenon of drawing the line and cause abnormal oscillation frequency switching transformer issued a " creak " sound and .

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