Precautions and methods of automobile computer maintenance

Category:Automobile engine repair - Date:2015-11-01

with the development of modern automotive electronics technology, in the automotive air conditioning system, whether it is manual control or automatic control of air conditioning, the cutting and joint of the electromagnetic clutch of the compressor is generally controlled by the computer.

there are quite a few failures on the computer during the maintenance of air conditioning system. When all the sensor signals can be input to the computer normally, if the computer can not correctly control the separation and engagement of the electromagnetic clutch of the compressor, the fault location mostly occurs in the 1 switch - acting triode in the computer.

if we want to repair the computer, we must first confirm that it must be a computer failure, so as not to blindly repair, cause unnecessary waste of time and cause other circuit failures. The maintenance of computers is based on theoretical basis and scientific method. It is by no means blind and reckless. Therefore, after repair, the computer can promise the warranty period.

maintenance of most computers' air conditioning control failure is actually replacing the related switch triode in the computer. Next, take Honda accord 2.2 sedan as an example to introduce the methods and steps of computer maintenance.

The first step is to find the connection end of the electromagnetic clutch control coil and the computer and the grounding end of the computer according to the circuit diagram. It is better to mark the terminal with the color pen.

The second step is to use the digital multimeter to measure and break off, from the determined air conditioning control terminal, a little bit down the computer's printed circuit, until a triode or tri tube row is found.

The third step is to determine the 3 pins of the transistor or the triode. The NPN transistor is commonly used in the computer. Here we take NPN as an example. The corresponding pin on the printed circuit is the collector of the transistor. The corresponding printed wire beside it is the base of the transistor. Of course, we need to further confirm whether it is left or right. The confirmation method is as follows: the air conditioning operation panel is set in the condition of refrigeration operation of the air conditioner, the voltage shift of the multimeter is connected to a base line to be confirmed, the A/C switch is opened, and the 5V should be displayed, 0V should be displayed when the switch is closed. The two lines are tested by this method, and the base is confirmed repeatedly. When the emitter is confirmed, generally if it is a triode tube, its emission is much more at the end of the row, and the end of the computer is connected to the end of the computer with the measuring and breaking end of the multimeter, and the other end is connected to the end of the ground which is considered to be a row, and the pin that can guide is the emitter of the triode. If there is only one transistor, it can be recognized easily by the thickness of the printed circuit.

The fourth step is to find the replacement triode. The replaceable triode may be an independent triode (Nissan), or a triode (Xia Li) directly embedded in the circuit board, or a triode (Honda) in a triode row. Such transistors can usually be found in the old automotive electrical components. The methods can be roughly summarized from the following aspects.

(1) look at the model. The type of triode made in Japan is generally 2SA (NPN), 2SC (NPN) and 2SD (PNP). The replacement components that can be bought in the domestic electronic market are BT179 and BT178. The type of the triode tube is generally 2003 and 1413.

(2) look at the appearance. This kind of triode should have 3 feet. The shape of the triode should be basically the same as the original triode. Generally, it is a flat triode.

(3) look at the resistance. The base of three level tubes generally has a series of resistance. The resistance value of the base pole is similar to that of the original triode. The determination of resistance values is as follows: the numbers of brown, red, orange, yellow, green, blue, purple, gray, white and black are 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0, such as brown black and black representing 1000. Because the base of the transistor is controlled by the size of the current, and the voltage of the computer is fixed, we must use resistance to control the current. If the current passes through the assembly, the transistor will burn down, and the current will be too small to trigger it.

(4) measurement confirmation. The roughly determined transistor is removed from the circuit board, and the property of the transistor is measured by the diode gauge of multimeter. According to the properties of the triode, only 1 pins should be connected to the other 2 pins, and this property can be used to determine the triode, and only one pair of pins is a field effect tube. The other two pins are the base of the transistor. Then select the measuring gear of the triode of the digital multimeter, insert the base of the triode into B, and the other two feet are inserted into C and E respectively. If the display value is between 200~300, it is proved that the pin is inserted, the C represents the collector, and the E represents the emitter. To determine whether the transistor is PNP or NPN. P is the positive pole, and N is negative.

the fifth step is to weld the selected triode to the circuit board. For transistors directly embedded on the circuit board and independent triode, the old parts need to be removed. For the triode row, it is necessary to use a screwdriver to break the base line of the triode, use the digital multimeter to measure and break the block, use a positive and negative pen to hold the collector and emitter of the triode, connect the base pole to the base control line of the circuit board, open the air conditioner, see if the multimeter shows the conduction, and if the guiding principle proves the three poles. The tube can be used. After that, the replacement parts can be welded to the circuit board, and the connection of the triode rows is welded from the back of the circuit board. Attention should be paid when welding: to judge the properties of the pin, and to avoid overheating as little as possible. After the completion of the welding, the feet should be measured by the multimeter. Finally, the additional triode should be wrapped with tape to avoid friction and connectivity with the computer.

The last step is the test. The computer is connected to the body wiring harness without installing the guard plate, and the air conditioner is started to see whether the electromagnetic clutch of the compressor can be absorbed or disconnected. At the same time, you can touch the transistor with your hands. Some heat is normal. If you are hot, it will be a problem. And let's see if the fault light is lit. If the air conditioning compressor is pulled in, the fault lamp will light up, indicating that the emitter of the transistor is wrong. If the compressor fails to shut down, it indicates that the triode that has been replaced or the base of the triode tube is not completely cut off. In the test, it is best to make the air conditioning system run more than 30min, see if the computer can work properly, carry out the road test above 10km, and see if there is a fault light on. If there is no problem, you can turn in the car. In addition, the best in computer maintenance within the inner fender down time for maintenance and specific markers for future reference.

the computer is a valuable part of the automobile. The breakdown of the computer that is introduced above is very difficult to directly observe with the eye. Therefore, the maintenance of the computer must have relevant electronic knowledge, through the scientific means of careful search and maintenance, otherwise it will only be contrary to the desire, causing unnecessary losses.

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