Graduation Thesis-Maintenance of Automobile Anti-theft Device

I. Preface:

Automobile anti-theft system is widely used in modern cars and plays a very important role in automobile anti-theft. It has the functions of automatic alarm system, preventing the car from starting after unauthorized personnel enter the car, and automatically locking the door. It is an indispensable device in the automobile anti-theft system. Automobile anti-theft system refers to an electronic system embedded in the main circuit of an automobile to prevent the automobile from being stolen or destroyed. The earliest anti-theft device, it mainly relies on locking clutch, brake throttle or steering wheel and shift lever to achieve the purpose of anti-theft, only anti-theft without alarm. In order to make up for this shortcoming, the electronic alarm anti-theft alarm device with remote control device came into being. The following is the whole process of my maintenance/installation of electronic burglar alarm. Let's discuss it.

Second, keywords: remote control, anti-theft device host, positive and negative trigger, troubleshooting.

Third, the text:

1. Question: On the 20th1117th, I received the task of repairing a Chevrolet Le Yue burglar alarm. After receiving the task, I first checked the fault and found that there was something wrong with the remote unlocking of this car. To unlock, the remote control must be placed under the dashboard.

Fault analysis: the remote unlocking of burglar alarm can't be controlled, but the short-distance unlocking can be controlled for the following reasons: ① the host and signal receiving antenna of burglar alarm are faulty, which leads to the weakening of signal receiving sensitivity of host (unlocking); ② The remote unlocking signal of the burglar alarm is weak, which makes the host computer unable to receive the unlocking signal (long distance).

2. Troubleshooting process: According to the above fault analysis, first check the host and antenna, and find that the antenna is well connected, but it is sensitive at close range, which also shows that there is no problem with the antenna and host control part. After checking the antenna and the host, check the remote control part. Because the remote control lock works normally, it means that the power supply of the remote control is not short of electricity. According to the above inspection results, it is concluded that the remote controller (unlock) is faulty. Because the functions of this anti-theft host and the remote control do not match, and the owner only has this remote control, it is recommended that the owner replace a set of anti-theft devices. With the consent of the owner, the anti-theft device of this car will be replaced. Before replacement, the old burglar alarm should be removed, and the following points should be paid attention to: ① Before removal, the control wiring harness of the old burglar alarm should be searched and classified, and then the old burglar alarm should be removed; (2) After the old burglar alarm is removed, the thread should be wrapped to prevent short circuit, and then the control wiring harness of the new burglar alarm should be installed in turn. When installed in the control circuit of the central lock, the central lock is wired in the way of "negative trigger" in the old burglar alarm (as shown in figure 1). After the test, it was found that the central control door lock could only be locked but not opened. At this time, the fault is analyzed, and the analysis results are as follows: There are several reasons why the central control cannot be unlocked: ① the anti-theft host has no signal output or the output signal is wrong; ② The central control computer is damaged; ③ The motor circuit is short-circuited. According to the above analysis results, start to check the signal output of the host. (Inspection method: Connect the power supply and signal output line with the test lamp at the same time. When the anti-theft remote unlock key is pressed, the test light should be lit, otherwise no signal will be output. ) find that the computer signal output is normal, so as to eliminate the fault of the computer host, and then check the motor. Because the motor works normally when it is locked, the motor is unlocked and locked with the same two lines, and only the positive and negative poles change, so the circuit fault of the motor can also be eliminated. At this point, the central control computer is left. First of all, the central control computer has locked work instructions. The power supply and bottom line, lock signal line and motor line of the central control computer are all normal. Because if these places fail, locking is impossible, and there is no problem, only the unlocking signal line of the central control computer is left. First, look at whether the central control unlocking works, and the result is negative, because the car can be unlocked before the anti-theft device is changed, which also shows that the central control computer is normal, so the central control computer should not be broken (but damage is not ruled out). I found the old burglar alarm again and made a comparison. It was found that the unlocking signal line of the old burglar alarm had a fuse of 15A, but it was not locked. According to the understanding of fuses, fuses are generally used for positive power supply. A fuse like 15A can indicate that this line has to bear a lot of current, and only the unlock signal can have this fuse. Through the above judgment, it shows that this line should be a positive power supply line. At this time, I decided to use the jumper positive power cord to this signal line (when jumping, we should consider the safety of the jumper to avoid short circuit. I use this method because I am familiar with the internal work of the central control computer and know whether the jumper will damage the parts. When the positive power supply jumper, the central locking suddenly works, which is exactly the same as my own analysis-this signal is controlled by the control mode of "positive trigger" (Figure 2). Because the positive trigger is used for unlocking and the negative trigger is used for locking, only the positive trigger and the negative trigger (as shown in Figure 3) can complete such control work in the anti-theft control mode, so the positive trigger and the negative trigger are finally selected for wiring control of the central door lock. After using the positive and negative trigger wiring, the central control door lock switches normally. Originally, the central control computer of this car is different from others (others usually trigger either positively or negatively), and it is positive and negative trigger control, so it breaks the conventional installation method. After the installation, the system was carefully checked and accepted, and no other faults were found. By this time, the fault that the central control door lock can't be opened by remote control has been completely eliminated.

Conclusion: From the above maintenance, we can see that my maintenance experience is still insufficient, for example, there is no test signal during disassembly. During the installation, there was no inspection, and the wiring mode of the old system caused these problems. I believe I will take a warning.

Verb (abbreviation of verb) Thanks: Thanks to the teachers and classmates who gave me guidance and support in writing this article. I would like to express my heartfelt thanks here!

References for intransitive verbs:

1, class notes of Dongfeng Automobile Institute

2, iron universal anti-theft device installation circuit diagram