(a) the tools and instruments needed to repair the car burglar alarm.
In addition to some commonly used tools, such as offset press, sharp tweezers, 10 screwdriver, medical needle, soldering iron and multimeter, the following tools and instruments should be provided for the maintenance of automobile burglar alarm.
1. Power supply for alarm maintenance The car burglar alarm is faulty and must be removed from the car for maintenance. Therefore, maintaining a regulated power supply is one of the necessary means. Generally, DC regulated power supply with continuously adjustable output DC voltage between 0 ~ 24v and output current above 2A can be selected (such as WYJ30V2A, TXDL77 1 1-2). These regulated power supplies are dual-meter output display, with over-current protection function and safe use. If a self-made regulated power supply is used, it is best to add an overcurrent protection circuit or display the output current.
2. Oscilloscope Oscilloscope can be used with 20MHz single-channel or double-channel oscilloscope. It is mainly used to observe the clock oscillation of CPU in the host computer of burglar alarm, the reception oscillation of remote controller, the demodulation pulse waveform, the pulse width modulation waveform of remote controller, the oscillation waveform of transmitting tube, etc. Of course, it can also be used to measure AC and DC voltages. Without spectrometer, oscilloscope is an indispensable instrument.
3. Self-made maintenance fixture The automobile anti-theft alarm is a multi-accessory alarm system that integrates various alarm function detection inputs and various control function outputs. All accessories are installed in the car, and some accessories are the electrical and pneumatic components of the car itself (such as direction lights and door switches). When repairing the alarm, the system accessories cannot be removed together. Therefore, the self-made maintenance fixture is also the preliminary preparation for the maintenance of automobile burglar alarm.
Maintenance tools indicate various control actions with indicator lights or LED light-emitting tubes, and simulate various detection inputs (such as door switches and key switches) with switches. By toggling the corresponding switch, the change of the indicator light of the anti-theft device in different states can be observed intuitively and clearly.
Figure1-1is the maintenance fixture used by the author during maintenance, and it is for reference only. Various control actions are displayed by LED. In order to facilitate identification, you can choose different colors of led. Insert the LEDs side by side on a small piece of cardboard or waste circuit board, indicate the representative control function at the bottom of each LED, and output lead wires with different colors (or paste notes on the lead wires) for easy identification. The current limiting resistor is connected in series with the wire and wrapped with insulating tape. The analog switch is a small push-type self-locking switch. The switch can be connected in series in the middle of the lead-out, wrapped with insulating tape, and labeled with words, and it can be used normally.
Of course, if readers are interested, they can use 12V instrument indicator light as control display, toggle switch as analog control, fix it directly on PVC panel, use aluminum alloy as frame, and use computer lettering recognition, and a more formal maintenance and inspection tool will be completed.
In addition to the tools and instruments described above, as a professional maintenance, a 500MHz spectrometer is also required to receive and observe the RF spectrum of the remote controller and the oscillation spectrum of the receiver, so as to adjust the same frequency matching between the remote controller and the system host. As an amateur maintenance, because the spectrometer is more expensive, there is no need to buy it specially.
(2) How to judge the approximate location of the fault according to the fault phenomenon?
1. Master the circuit structure of the automobile anti-theft system. Although different manufacturers and models of automobile anti-theft alarms use different components and have slightly different circuit forms and software functions, their basic circuit structures are the same. Figure 1-2 and figure 1-3 are the principle block diagrams of typical coded and code-hopping car burglar alarms. Memorizing the schematic diagram of the circuit is very beneficial for analyzing and understanding the schematic diagram of the automobile anti-theft system and quickly judging the approximate range of the fault.
In actual maintenance, firstly, according to the fault phenomenon, it is judged which component or components caused the fault, then the components caused by compression are checked, and the faulty components are further repaired with the power supply as the starting point and the signal flow or control flow as the clue.
2. Master the fault law of each part of the circuit. Overhauling the car burglar alarm is the same as overhauling other household appliances. The abnormal operation of each part of the circuit shows the fault phenomenon, which always has its regularity. Mastering these rules is very helpful to quickly and accurately judge the approximate location of the fault, and beginners had better remember them.
The local circuit of the car burglar alarm is not working normally, and there are generally the following rules.
(1) power failure law. There is a fault in the power supply, which generally shows that there is no response after power-on, the light does not flash, the relay does not act, and the system is in a "dead" state. +5V voltage is the focus of fault inspection during maintenance. If the +5V voltage is normal, the power supply voltage is basically normal; Otherwise, the power supply circuit is abnormal.
(2) Failure law of remote control receiving circuit (receiving head). The performance is that the remote control is ineffective and the remote control distance is short. The fault diagnosis of the remote controller receiving circuit focuses on the signal output end of the receiver. By observing the clutter reaction at the signal output and the presence or absence of low-frequency pulse signals when transmitting signals, we can judge whether the receiving circuit is normal or not.
(3) The fault law of decoding circuit fault. The failure of the decoding circuit indicates that the remote controller is not working. The fault check point of the decoding circuit is whether there is a signal at the output end of the decoding circuit. For example, there is a pulse data signal input at the input end of the decoding circuit, but the level at the output end of the decoding circuit has not changed, indicating that the decoding circuit is faulty.
(4) 4) Failure law of CPU circuit. The failure of CPU circuit is characterized by no response after power-on, disorder of system control function, and partial or total failure of system control function. One of the quick ways to check whether the CPU circuit is normal is to connect the door detection port of the anti-theft system to a low level and listen to the pull-in sound of the relay in the machine. If there is no response, the CPU circuit is faulty.
(5) The driving circuit has a failure rule. If there is no output from each driving load (such as hollow lock, double jump light, alarm horn, etc.). ), indicating that the load drive circuit is faulty, probably because the drive chip itself is damaged; If only one load does not work, check the control circuit of this load.
(6) Fault regularity of alarm detection input port and function execution control output port. Indicates that a detection function (or control function) does not work or always performs a control function. By checking the level state (normal and dynamic change) of the input (or output) port, it can be judged whether the fault location is the internal circuit damage of CPU or the external circuit damage.
3. Distinguish whether it is an internal fault of the system host or a system accessory fault. There are many accessories in the car burglar alarm. When overhauling, first disassemble the accessories and then disassemble the main engine, which can sometimes get twice the result with half the effort. The following describes the troubleshooting methods caused by the outside of the machine.
(1) The system is not responding. Check whether the system power supply is normal, whether the fuse of 12V incoming line is blown, whether the fuse holder is in good contact and whether the system grounding is good.
(2) If the alarm horn doesn't ring, check whether the grounding terminal of the alarm horn is intact and whether the alarm horn itself is normal. Connect the positive pole of the alarm speaker directly to the positive pole. If the alarm horn doesn't sound, there is something wrong with the horn.
(3) If the car double jump light is not on, check whether the output fuse is blown and whether the external diode is damaged.
(4) Call the police when entering the anti-theft state. Check whether the door switch and the front cover switch are damaged and detect whether the sensor is faulty.
(5) If false alarms frequently occur in the anti-theft state, check whether the detection sensor is too sensitive, readjust the detection sensitivity or unplug the sensor for verification.
Second, the problems encountered in the maintenance and solutions
(1) How to draw the circuit schematic diagram of the automobile burglar alarm?
Like the maintenance of other household appliances, the maintenance pattern is very necessary, especially the circuit schematic diagram. With the circuit schematic diagram, you will have 50% confidence and grasp when dealing with faults. Especially in dealing with some difficult faults, if there is no circuit schematic diagram, it will directly affect the maintenance efficiency, or even can not be repaired. Schematic diagram is especially important for beginners.
However, when automobile anti-theft alarm products are sold, they generally do not provide pattern information, and there are few books introducing this aspect. All the related patterns in this book were drawn by the author himself. The following introduces the method of drawing the circuit schematic diagram. If readers need this, they can also contact the author and I can draw it for you.
1. General drawing method of circuit schematic diagram of single-sided PCB direct-inserted components
(1) First, paint the solder joints and PCB traces (including short wires) of components connected with the positive electrode of the circuit board with a colored pen, and paint the solder joints and PCB traces (including short wires) connected with a large area of copper foil ground wire (negative electrode of power supply) with a blue colored pen.
(2) Starting from the local circuit, you can use one page for one part or one page for multiple parts. What is the core of each part is determined by your own habits.
(3) Starting from the hand of the connector, taking each terminal as a clue, each component is marked with a nominal value, and those with component labels are also marked together, and those without labels are not written. When drawing, draw one contact at a time. When a node is complex, you can first draw one end pin of all components of this node, and the other end of the component is temporarily empty. Draw a node, and then draw another node.
(4) With CPU as the core and each pin as the clue, draw the peripheral components of each pin one by one. Direct connections that can be directly connected with the (drawn) connector part, and those that cannot be connected (because the diagram is too messy, or there is no space for direct connection, or not on a page) should be marked with the same network number (such as A, A, B, B, VCC, 5V, etc.). ).
(5) Take other integrated circuits and transistors as the core and the pins of integrated circuits and transistors as clues to draw their own external components. The above is only a sketch of each part of the circuit. In order to prevent the phenomenon of missing drawing and redrawing, when drawing a circuit node, all the component pins connected to this node must be drawn, and the drawn components should be marked with a pencil. After all components are marked, it means that all components have been checked.
(6) Check the sketch. Connect the local diagrams into a whole to see if it conforms to the logical relationship of the circuit, and then check the sketch with the physical diagram again (if there are irregularities in the circuit diagram, it should be checked repeatedly as a key point) to correct errors or omissions.
(7) Arrange the sketch into a standard circuit diagram. 1) circuit symbols and comments should be correctly standardized. 2) The power supply path and signal direction of components should be clear and intuitive. 3) The layout of circuit symbols should be reasonable, the arrangement should be as neat and beautiful as possible, the words should be clearly marked, and the arrangement between words should not be too crowded or scattered.
2. Drawing method of circuit schematic diagram of surface mounted components on double-sided PCB It is difficult to draw circuit schematic diagram with double-sided PCB, and some components must be removed from the circuit board before drawing. Before disassembling components, the component layout diagram of PCB board should be drawn first, and the component parameters should be indicated for recycling. Its drawing method is the same as that of single-sided PCB.
(2) How to find the position of each main chip and the function of each terminal of the connector without the circuit schematic diagram.
Although there are many models and brands of car burglar alarms, their detection function and control function are the same, and they all input and control the same output object through the same detection method, but the style, quantity and arrangement order of connectors are different. So they have many laws in circuit structure and component application. Mastering these rules is of great benefit to quickly find faults and draw circuits.
When we turn on the main engine of an alarm, the first thing we see is a row of relays (generally not less than three) and several eye-catching integrated circuits. According to the model of integrated circuit, it is not difficult to judge the function of each integrated circuit. It must be a CPU with a 4-pin package, a CPU with a PICXXXX character model at the beginning, and a general CPU is plugged into a socket; The decoding chips are named after AX5327, PT2272, VD5026, etc. The ones with address coding pads on pins ①-⑧ are the decoding chips; The driver chip is named after XX2003XX and other models. The remote control receiving circuit is generally an independent PCB small board; Alarm speakers and wireless transmitters are sometimes controlled by transistors, and commonly used models are B772, TIP42C, etc. Through observation, the above law is not difficult to find. The following describes how to find the function of each terminal without circuit diagram and wiring diagram.
1. Control output terminal In general, the control output terminal is on the same connector, and it is a Dalian connector.
(1) power input. The thick red line is the input end of 12V power supply, the moving contact of the double-contact output relay (double-jump lamp relay) is directly connected to 12V, and the moving contact of the alarm speaker relay (or the emitter of PNP electronic switch tube) is directly connected to 12V.
(2) negative pole of power supply. The black thick line is the negative pole of power supply, the large area copper foil of circuit board is the negative pole of power supply, the negative pole of large filter capacitor is the negative pole of power supply, and the middle pin of three-terminal 5V stabilized IC is the negative pole of power supply.
(3) output end of central locking. The output end of the central control lock is adjacent to the 6-terminal, which is characterized by finding two relays of the same model, which are generally closely adjacent. For example, the six contacts of these two relays are directly connected to the output terminal, which is the terminal of the central locking device.
(4) Alarm speaker output. Check the voltage of the remaining output terminals with a multimeter. If it is found that a terminal has no+12V output in the silent anti-theft state and+12V output in the audible anti-theft state, it is the output terminal of the alarm speaker.
(5) Double-jump lamp output end. The two terminals directly output by the double-contact relay are the control output terminals of the automobile double-jump lamp. For the vehicle with single-ended relay output, the voltage of each output terminal can be measured in the alarm state (or in the flashing state when the door is opened), and the terminal with 12V jump level is the control output terminal of the automobile double jump lamp.
(6) Drive the output end by cutting off the fire source. In the alarm state, measure the grounding resistance of each terminal. If the resistance drops sharply in the alarm state, the terminal is the driving end of the external relay.
2. Detection input The detection input is generally on the same connector, generally a small connector (relative to the output control terminal).
(1) gate detection input. Use a multimeter to measure and detect the normal level state of each terminal at the input end, and connect the high-level terminal to the low level at ordinary times; Connect the low level terminal to the high level. At this time, no matter whether the system is in the disarmed state or the anti-theft state, if the terminal that controls the double-jump lamp of the automobile has an output, the terminal is the door detection terminal. High level is valid for positive trigger gate detection input, and low level is valid for negative trigger gate detection input.
(2) Key switch detection input. Use a multimeter to find the input terminal which is usually low level and connect it to high level. If it doesn't work in the disarming state, but it can trigger an alarm in the anti-theft state, it is the key door detection terminal; If this high level is connected with the high level first, only the central locking action will occur when the remote control anti-theft release function key is operated (the double jump light and alarm horn are unresponsive), indicating that this terminal is a key switch detection terminal.
(3) Foot brake detection terminal. In the anti-theft state, connect the detection terminal of the key door to high level, and connect other detection terminals which are usually low level to high level. If the central lock is related to the lock action, this terminal is the foot brake detection terminal.
Handbrake detection terminal, high voltage detection terminal and remote starting output terminal are only provided in remote starting system. Hand brake and high voltage detection terminal can be found by using their own characteristics or the above exclusion methods. It is not difficult to confirm that the remote starting output terminal is usually output separately through the 3P connector.
LED indicator light and sensor detection port are generally output through small connectors, which are easy to identify.
(3) Problems needing attention in maintenance
1. When the fuse of 12V incoming line is found to be blown, check whether there is a short circuit fault in the system before replacing the fuse. The replacement fuse shall not exceed the original specification, so as not to burn the car line.
2. Before maintenance and electrification, pay attention to check the supply voltage of the power supply and observe the current situation. Only when there is no short circuit inside the system host can it be powered on for a long time. The system host current is generally less than 20 ~ 30mA when the load is not connected.
3. Carry out maintenance according to the normal maintenance sequence. When checking the "No" fault, it should be overhauled in the order of "+12V voltage →+5V voltage → system control CPU→ drive circuit → remote control receiving circuit → decoding circuit".
4. When the power supply is checked for "no" fault, do not adjust the adjustable components unrelated to it, such as adjustable capacitors and adjustable inductors.
5. Don't disassemble and weld components with electricity, and don't plug CPU or other integrated circuits with sockets when there is electricity.
6. When removing the multi-pin components from the double-sided PCB, you must be careful not to pull them.
7. When measuring the voltage at a certain point of the circuit, be careful not to short-circuit the adjacent solder joints (such as the adjacent pins of the integrated circuit and the pins of the transistor) due to the sliding of the stylus. It is best to fix the negative pole of multimeter to the negative pole of power supply and measure the voltage with a single stylus.
Third, the common maintenance methods
After identifying the faulty parts or components, appropriate methods can be used for inspection and verification. Like other electrical appliances, the most effective overall method is the maintenance rules from the outside to the inside, from easy to difficult, from brain to hand, from general to special. Common maintenance methods include visual inspection, voltage test, current test, signal injection, signal tracking and so on.
1. Visual inspection is the use of human sensory organs, such as eyes, ears, nose and hands.
In order to find the faulty parts, visual inspection is generally a hard fault.
(1) Visual inspection before power on. Before power-on, check whether the fuse of 12V incoming wire is blown, whether the connector is firm, whether the circuit board has burn marks, whether it is soaked in water or oil, whether it is soldered or disconnected, whether the voltage stabilizing IC, integrated circuit and transistor explode, whether the electrolytic capacitor leaks or bulges, and whether the relay shell has burn marks.
(2) Visual inspection after electrifying. If no problems are found by visual inspection before electrifying, electrify for inspection. First observe whether the current of the whole machine is too large, and then power on for a long time for maintenance. Pay attention to observe whether there is any peculiar smell or smoke when power is on, and whether there is any heating sensation on the hand-held voltage-stabilizing IC, integrated circuit and transistor.
2. Voltage test method Voltage test (quantity) method usually refers to the inspection and measurement method of DC voltage. The most effective method is to detect the voltage of each pin of the integrated circuit and transistor in the machine and compare it with the normal value as the basis for judging the fault. However, as the voltage of some basic conventional circuits, we should have a general understanding.
The turn-on voltage of (1) LED is about 1.8V, and the turn-on voltage of silicon diode is about 0.6V (germanium diode is generally not used in anti-theft system). The voltage between the base and emitter of the transistor (silicon tube) in the amplified state is 0.6V, and the collector voltage cannot be close to the power supply voltage or several tenths of volts. When the emitter and base of PNP transistor are close to equal potential, there is no output voltage at the collector. When the base voltage of the switching NPN transistor is 0.6~0.7V, the collector voltage should be lower than 0.3V. ..
(2) The power supply of decoding integrated circuit, CPU and memory is generally +5V, and the reset terminal voltage of CPU should be close to +5V (low level reset mode). If the input terminal of the driving integrated circuit is high, the output terminal is low; If the input is low, the output is high.
(3) voltage comparator, when the reverse input terminal voltage is greater than the noninverting input terminal voltage, the output terminal is low; When the terminal voltage of the inverting input is lower than that of the noninverting input, the output terminal is high.
(4) The low level effective detection end is generally high level, and the high level effective detection end is generally low level.
(5) If the voltage of one pin of the CPU is lower than the normal value or 0, check whether the pull-up resistor is open, and whether the anti-interference capacitor leaks or breaks down.
3. current test method current test (quantity) method usually refers to DC measurement method. Current measurement is mainly to measure the total current of the system host or accessories, or the total current of an integrated circuit. The decoding IC and PIC series CPU adopt CMOS technology, and the static current is microampere. If the measured current is more than a few milliamps, it is necessary to consider whether the integrated circuit is damaged.
4. Resistance measurement Resistance measurement is one of the most basic and extensive detection methods. Generally, the method of on-road measurement and independent measurement is adopted.
When measuring the resistance of the resistor in the circuit, due to the influence of other parallel circuits, when the resistance is low, it is not necessarily that the component is damaged, so it needs to be removed from the circuit board and measured separately. Resistors, diodes, etc. It can be measured by disconnecting a pin. If the resistance measured on the road is greater than the actual nominal value, it can generally be considered that the element has been damaged.
It is more accurate and reliable to measure the on-off of wires, printed boards, inductors, connectors and microswitches on the road.
5. Signal injection method The most commonly used signal injection method is to check whether the AC path of the amplifier is smooth by using the human body clutter signal, which is an effective method. However, it should be noted that this method can't help the detuning of frequency selection circuit and resonant circuit. The signal injection method can only be used if there is a terminal display device. When the electronic sensor is overhauled, the human body clutter signal is injected from the background to the foreground, and the status of the led indicator light is observed, so that the fault position can be quickly found.
Of course, it is better to use various signal sources (such as low-frequency signal transmitters) as injection signal sources.
6. Signal tracking method The signal tracking method is usually used in conjunction with the signal injection method to track the receiving and amplifying circuits according to the signal cycle order. For example, when checking the remote control receiver, the VHF signal generator can be used as the signal source, and the oscilloscope can be connected to the signal output end of the receiver from the collector of the high amplifier tube. Corresponding waveforms should be observed at the input and output terminals of all levels of circuits.
When checking the receiving circuit of the ultrasonic circuit, you can use the ultrasonic transmitter as the signal source and use the oscilloscope to check the receiving and amplifying circuit. When overhauling the ultrasonic transmitting circuit, the AC signal waveform can be measured from the oscillating circuit (taking the oscillating stage as the signal source), the amplifying circuit and the ultrasonic sensor.
7. Parallel test method Parallel test method means that when there are suspected damaged components in the circuit, components with the same specifications can be connected in parallel to the suspected components for verification. The parallel test method is only applicable to open-circuit or failed resistance-capacitance components, not to short-circuit or leakage components, nor to integrated circuits or transistors, so as not to damage the devices.
8. Component replacement method Component replacement method is to replace a suspected faulty component with a good component to verify whether the component is damaged. There is no way to replace the component. When repairing the car burglar alarm, the components that are usually replaced are memory, crystal oscillator, acoustic surface resonator, resonant circuit, patch capacitor of oscillating circuit, etc.
9. Separation inspection method Separation inspection method is to separate a part or a component of the circuit from the whole circuit and judge whether it is faulty. This method is the most effective method to check the load current fault. If the +5V load has an overcurrent fault, the decoupling filter capacitor, the power supply current limiting resistor or the power supply pin of the integrated circuit can be removed respectively, and even the power supply of a certain part of the circuit board can be cut off. If the fault is eliminated, the overcurrent fault will be in the part of the circuit that has just been disconnected.
10. Knock vibration method Knock vibration method is to find the fault position by knocking and vibrating some components or circuit boards to make the fault phenomenon disappear or reappear. This method is suitable for intermittent faults such as virtual welding and poor contact. It is common for relay contacts to burn out and have poor contact, and faults will be found quickly by this method.
Common faults and solutions are available, take your time ~