For input signal without boot image, first of all to the following reasons: QXjservice manual download site
 QXjservice manual download site
1, abnormal voltage input, which leads to the circuit has no job. QXjservice manual download site
 QXjservice manual download site
2, video switch is damaged, the video signal can't switch 3, bus circuit is unusual, unable to control the IIC bus. QXjservice manual download site
 QXjservice manual download site
Repair process: QXjservice manual download site
 QXjservice manual download site
1, for normal boot character display, input signal abnormalities, first enter the self-checking, self-check result shows AVSW1NG, AVWS NG, TUN1 NG, TUN2 NG, DAC3 NG, MSP NG, SOU NG. For so much detect abnormal, first consider whether the voltage loss, caused by the integrated circuit has no job, so to measure the working voltage of the circuit one by one, measuring SUB5V, BT30V, MAIN9V, SUB3.3 found no abnormalities. QXjservice manual download site
 QXjservice manual download site
 QXjservice manual download site
2, in the case of a voltage have no problem, the second is to consider the element damage, if there is a bit unusual, can consider to corresponding bus circuit is damaged, but the damage phenomenon of so many parts are unlikely, so consider directly to the bus. During the inspection found that these circuits are hanging in the bus when the bus IIC1, so IIC1 for voltage measurements, look to whether IIC bus disconnected. After measuring the voltage for 4.5 V, for SCL1 SDA1 is 5 V, oscillating signal in pointer table, so maintenance into temptation. So will have to search for, drop by and used the oscilloscope measurement, direct measurement of the main CPU IC1104 98 feet, 99 feet, bus signal waveform is normal. QXjservice manual download site
 QXjservice manual download site
3, after the bus is on the main CPU output bus by IC1109 after plastic buffer, then measure 19 feet, 20 feet of IC1109, found that the waveform is a bit messy, doubt is IC1109 bad, after replacing IC1109 troubleshooting.QXjservice manual download site