According to the phenomenon of grating is dark, the first detection of three video output amplification integrated block IC351 and peripheral circuit, see figure. Measurement IC351{1}, {2}, {3} feet video signal input terminal voltage is 1.8V, {5} feet (in-phase input) and {6} feet (depending on the level 221V power supply voltage end) voltage is normal, but the {7}, {8}, {9} feet (B, G and R output end of the voltage was about 205V and normal value is about 150V), visible grating dark caused due to {7}, {8}, {9} feet high voltage. Check IC351 peripheral components are not damaged, the measured IC351 each foot of positive and reverse resistance value is basic and normal, it is estimated that does not damage the IC351, IC351 not in amplification of the normal working state, but is in the off state.
Along the B, G, R input signal forward checking, IC3401{12}, {14}, {16} pin voltage respectively 1.9V, 2.0V, 1.8V, normal 3.6V, 3.5V, 3.6V; {6}, {3}, {1} pin voltage 1.7V, 1.7V, 1.6V respectively, normal values of 3.5V, 3.4V and 3.5V. The normal power supply voltage 12V {5} feet. Re check IC601{19}, {36}, {50}, {59} and other power supply input pin voltage, are about 7.6V, while the normal should be regulated 9V power supply. Along the circuit board to D board examination and found that D in three terminal voltage stabilizing block IC805{3} output voltage 7.6v. {1} pin input voltage is 8V only, but the voltage at both ends of the C836 for normal 12V illustrate R842 drop is too large. Remove R842 check, R842 has changed from 4.7 to 14. After the replacement of the 4.7 / 5W resistance, the fault disappears.
Because of the increase in the resistance of R842, make IC601 supply voltage by normal 9V decline is about 7.6v, and IC601 both video processing and multi standard chroma decoding and line field synchronous separation, oscillator, incentives and other functions, causing the R, G, B video signal output smaller, caused by R, G, B amplification bias circuit change, CRT cathode and the signal voltage, electron beam base cutoff, so the grating in the dark. At the same time, the oscillating field is not normal, so to see the dark shadow glitter, left and right swing and drawing, oscillation frequency abnormal caused by transformer switch issued a "squeak" sound.