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Excavator computer board working principle and maintenance


Function Description:

(1) Excavator brand throttle computer boards that use DC motors can be replaced (such as Daewoo, Hyundai, Xugong, Liugong, Longgong, Sunward, Xiamen, Foton Lovol, Sany and other models). (If the electronic throttle function and the hydraulic board are on the same computer board, if the throttle part is damaged, the universal throttle board can also be replaced with the electronic throttle function).

(2) The peripheral wiring is as shown in the figure above, which requires an external power supply, 2 pressure switches, accelerator knob potentiometer, accelerator motor, and speed sensor. According to the wiring as above, it can have the electronic throttle function.

(3) The throttle can be increased or decreased through the throttle knob. After turning on the automatic idle speed switch, if the speed is above about 1200 rpm, the automatic idle speed adjustment will be carried out after 5 seconds. When any condition of the pressure switch, automatic idle speed switch and throttle knob changes, the automatic idle speed will be exited. Idle to the speed position set by the throttle knob.

(4) The number of flywheel teeth of different engines is different, so the detection of the speed signal will be different.

(5) The pressure switch is normally open type. That is, when the pressure switch is turned off, it is a necessary condition for automatic idle speed. When the pressure switch is turned on, it will exit the automatic idle speed when it is grounded.

(6) The speed sensor connection only needs to be connected in parallel, that is, there is no need to disconnect the original car line, just peel off the original car speed sensor wiring harness, and connect two wires in parallel.

2. Factors leading to damage to the computer board

The most common reasons for computer board damage are water ingress and mechanical impact. In addition, lightning strikes, welding surges, pin rust, and internal component ablation can also cause damage to the computer board. The usual way to prevent welding surge is to disconnect the power supply of the whole machine, that is, cut off the battery switch. Some manufacturers even require users to disconnect the computer board and the wiring harness of the whole machine before using electric welding. The most common cause of pin rust is the poor sealing performance of the large plug of the computer board, which leads to the immersion of water, and eventually leads to broken pins or poor contact over time.
Computer board damage generally has the following conditions:

1. The generator fails, resulting in high voltage in the circuit.

2. Connect the batteries in series when the user starts the engine.

3. Privately pulling electrical appliances indiscriminately, increasing the electrical load, and burning due to excessive current.

4. The generator regulator fails, resulting in excessive generator power generation.

5. The positive and negative electrodes of the battery are connected incorrectly, as well as the aging of the wiring harness and the poor short grounding.

6. If the maintenance is not in accordance with the operating specifications, the ECM is plugged and unplugged with power on.

7. The excavator cut the cable and suffered an external high-voltage electric shock.

8. Misuse of large-capacity fuses.

9. Water enters the computer board, resulting in a short circuit.

10. The wiring of the computer board is wrong or improperly inserted.
Three, the basic steps of computer board maintenance

To repair a relatively unfamiliar circuit board without any schematic diagram, the so-called "experience" in the past is very useful. Although the probability of repairing the circuit board is greatly increased with the help of the circuit online repair tester, if the method is not appropriate, Work is still half the effort. So, what can be done to improve maintenance efficiency? Summarize the following principles:

Principle 1: Look first and then measure

Tools used: digital (or analog) multimeter, magnifying glass

When holding a circuit board to be repaired, it is a good habit to first inspect it visually, and use a magnifying glass if necessary. What to look at? Mainly see

1. Is there any disconnection? Are there burn marks?

2. Are discrete components such as resistors, capacitors, inductors, diodes, transistors, etc. disconnected?

3. Is there any breakage or adhesion of the printed circuit board connection line on the circuit board?

4. Has anyone repaired it? Which components have been moved? Are there any mistakes in operations such as virtual soldering, missing soldering, and reverse insertion?

After confirming that the repaired board does not have the above conditions, first use a multimeter to measure the resistance between the power supply and the ground of the circuit board. Usually, the resistance of the circuit board is above 70-80Ω. If the resistance is too small, only a few or a dozen ohm, it means that there are components on the circuit board that are broken down or partially broken down, and measures must be taken to find the broken down components. The specific method is to supply power to the board to be repaired, and touch the temperature of each device on the circuit board with your hands. Those who are hot will be the key suspects.

If the resistance value is normal, you can use a multimeter for fault detection. Because there are many factors that cause the failure of the circuit board, the purpose of measuring the discrete components such as resistors, capacitors, diodes, triodes, field effect transistors, and DIP switches on the board is to first ensure that the measured components are normal and repaired. The principle is that the problem that can be solved with a multimeter, do not complicate it.

Principle 2, first outside and then inside, enumeration test

Tools used: HY circuit online maintenance tester series, marker pen

Because each model of the HY circuit online maintenance tester series integrates two fault diagnosis techniques, one is the standard comparison test method (ie ICFT) based on the device test program library; the other is the real-time comparison scan test based on the VI curve law (ie ASA-VI).

When using ICFT for chip testing, the following two test blind spots may appear:

1. The test program library has not yet established a test program for a certain chip, that is, there is no such chip in the library.

2. Even if the test program library has established the chip test program, the "online test" fails.

The computer board of the excavator is rarely damaged during normal use. It is not a wearing part, and is generally caused by man-made or force majeure. Generally, the reasons for force majeure damage are lightning strikes and ultrasonic interference. The working environment of the excavator is complex, harsh and changing, and the reasons for the damage to the computer board are also various. It is the first and foremost to take preventive measures in advance.