Digital video circuit is basically by microprocessor, memory, A/D and D/A converter consisting of large scale digital integrated circuit. Guarantee the normal work of the digital circuit prerequisites: (1) with normal stable working voltage. (2) there are normal power on reset and stable crystal vibration signal. (3) various correct input/output clock signal. So in troubleshooting must comply with the above three conditions, by testing the microprocessor with the pin of the potential of integrated circuits; Test point pulse temporal waveform; Look in line with the first power supply, then to the waveform, the principle of potential, can be reasonable in order to find out the fault point, troubleshooting as soon as possible.
 
 
In the digital video unit circuit board, with large scale integrated circuit and without pin components, so in repair if there is no more than 99% of the master, don't change the integrated circuit, because of the integrated circuit and microprocessor failure rate is very low. Especially the microprocessor, reliability and durability are relatively high. Most entities in microprocessor manufacturer curing control program. So a but damage cannot repair, also very difficult to replace. Remove the carelessly will damage the circuit board. Also should pay attention to integrated circuit in the replacement model suffix, even the same type suffix, replace the fault cannot be ruled out.
 
Digital integrated circuit and microprocessor, when doubt its damage, the first to test for a chip to the power supply voltage is normal. In many cases caused by power supply voltage is not normal, integrated circuit doesn't work, or even burned chip. So, in the maintenance work should focus on testing the first integrated circuit in the power supply, to see if the voltage stability of right, to avoid detours in maintenance. Then focus on potential detection chip of the pin, see its are consistent with the values specified. Moreover, test chips available oscilloscope waveform of each pin. In general, the damage of the microprocessor, integrated circuits, in addition to the pin voltage is not normal, the chip surface temperature were higher than that of the normal chip, so touch test its surface temperature also can yet be regarded as a rapid method for auxiliary judgment.
 
Microprocessor in CMOS devices and digital integrated circuit damage enemy for static electricity. The antistatic properties is very poor, electrostatic easy to damage to the device. Especially under the condition of dry and low temperature maintenance when it is best to circuit board with wire grounding, and before repair the human body to discharge, electric tools such as enclosure grounding conductor and application. In order to prevent the maintenance and disassembly, again by the human body electrostatic damage to the microprocessor and integrated circuit chip.
 
From digital video circuit maintenance, we summarize the analysis found that cause the camera no image, or images, the main reasons for the bad power supply not normal accounted for about 40%, device damage accounted for 20% (about 10%) reset circuit and pulse circuit, and human improper operation and poor panel switch is 30%. Poor contact circuit of about 10%. So before the overhaul to ask for details of the user. Find out the cause of the failure. And carefully check the camera external function position of switch is correct, contact of the switch on and off are in good condition. Then mount E power supply under normal conditions of measuring input B301 12 feet, output waveform B320 (1), (2), (3) feet. If the input is correct, the output is not correct, the circuit fault exists.
 
If the oscilloscope in the hand, can be an oblique wave generator, as shown. During overhaul digital video circuit as long as 12 feet to B301 is A/D converter (IC307 19 feet) enter A sawtooth wave signal, then all input and output of digital integrated circuit will also have A certain output pulse shape, very convenient for maintenance.
 
The sawtooth wave signal generator from Q1 to Q3 in the PNP transistor, optional 9011; Q4 ~ Q5 as NPN, optional 9012. This circuit can be made on a small circuit board, adjust the R2 output make the output stability of the saw tooth wave signal of 50 hz. With the circuit will be very convenient to help you repair more accurately M3000 / M9000 type machine digital video.