Because the screen has a flashing horizontal line, it is suspected that the field scanning circuit is not normal, but the search field scanning circuit is not found fault. Turn check power supply, switch power supply output voltage is also with the sound down jitter, doubt sound resounds when switching power supply is closed instantly, check the standby CPU control end {18} feet and degaussing relay control end {24} pin voltage, were also appear jitter phenomenon, indicating that the above speculation is correct.

In order to find out the cause of the CPU flash, the power supply voltage of 5V is normal and stable, and the {36} pin voltage is normal. The CPU is a I2C bus control, the normal operating conditions in addition to the power supply voltage, reset voltage and timely clock oscillation must be normal, I2C bus must also be normal. Therefore, the voltage of the SDA ({54}) is normal, and the SCL ({56}) is detected, and the voltage is less than 2V and it is not stable. Disengage {56} feet outside circuit measuring pin Voltage 5V, and the outer circuit voltage is still less than 2V, caused by SCL terminal voltage is not normal in the external circuit is described.

The machine is hung on the I2C CPU bus and then a multi block IC. In general, it is necessary to break down the corresponding pin of each IC in order to determine which block IC on the I2C bus is pulled down. If the I2C bus voltage is returned to the IC, the IC has a fault. Unplug the PIP circuit board (P board), the fault is still, for hanging on the I2C bus IC more, one by one to break open pin time-consuming. The investigation found that the corresponding pins of each IC were on isolation resistors are connected in, adopt measure the isolation resistance pressure drop across the way to judge. When the SCL (220) R333 () is found to be IC304{22} (), the pressure drop is about 0.1V, which is higher than the pressure drop of the other resistor. Taking into account the probability of IC damage is small, it is first to check the foot on the ground and the 5V regulator tube D015, found its reverse leakage. After the replacement of the test machine, the SCL terminal voltage rise, troubleshooting.