According to the phenomenon analysis, the fault is not in the system control circuit, is out in the power circuit. First check the power supply circuit, measuring power output connector "001" the foot of resistance is not abnormal, electrical measuring the connectors of the pin voltage were normal, indicating that the normal operation of the power supply circuit, accordingly, we can judge the fault in the system control circuit.

The control circuit of the machine system is composed of the main control microprocessor IC2001, the timer microprocessor IC7501, the function expansion block IC6801 and the peripheral components. System control circuit, the three pieces of integrated circuit coordination for the functions of video control and mutual transmission of information, the transfer of information is contained in the following two aspects: (1) the serial clock signal (clock), Ann is microprocessor synchronous signal, ensure the data accurate transmission and recognition; (2) is a serial data signal, microprocessor control.

The serial clock signal of the IC200144 pin is added to the IC750117 pin and the IC63012 pin, and the IC750118 pin is the serial data output end. If there is a problem between the three pieces of the integrated circuit, the video recorder will not work properly. Overhaul and test IC20011, and 8 feet and IC75011 pin voltage was 5V (normal); measuring the foot of the IC200145 resistance to ground to 4K, normal; measured 14 feet of resistance is only an 0.2K, significantly lower than the normal value 4.2K Omega, illustrate the serial clock signal formation or transfer fault in the circuit. Internal circuit according to the analysis, resulting in the abnormality of on resistance to the foot of the IC200114 reasons: (1) IC2001 pin 14 of the damage, damaging the internal circuitry (2) IC7501 17 foot; (3) IC6801 2 feet of the internal damage; (4) capacitance C6011 serious leakage. In order to determine the fault position, then by three IC from the corresponding pin, respectively to detect the resistance to judge. Disengaged IC2001 14 feet detected the foot of resistance normal 5.6 K, indicating that the internal circuit is normal; then cut IC6801 2 feet of the connection, the pin detection of resistance for 5.6 K, also normal, that C68012 feet the internal circuit is normal, then cut to the IC7501 of 17 feet connecting line, detect the foot to ground resistance is an 0.2K, that integrated block IC7501 17 foot internal circuit have been damaged.

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