Troubleshooting
According to the electrical system diagram of this type of excavator and the electrical wiring diagram of the cab, it can be seen that the D2 diode and several other diodes are connected to their respective lines in the form of connectors. Disassemble the rear panel of the cab and find three bundled yellow encapsulated diode connectors in the intricate wiring harness. Check the color of the connecting wire of the connector, and determine the D2 diode by comparing the color of the connecting wire (RB and RW) of the D2 diode marked on the electrical wiring diagram. It can also be determined by observing whether the battery relay cannot be closed after the D2 diode is removed when the engine is not started. Remove the D2 diode from the connector socket and measure with a multimeter. It is found that the resistance in both directions is 0Q, indicating that the D2 diode has been broken down.
Verify the failure point: start the engine, turn off the key switch, and the flame cannot be turned off normally; pull out the D2 diode, and then turn off the key switch, the engine will shut down normally. Prove that the judgment is correct.
The fault point was found, but there was the embarrassment of not being able to buy accessories (the details of D2 diodes are not on the parts catalog provided with the car). Analyze the working conditions of the diode: In the circuit, the D2 diode is mainly used to cut off the reverse DC 24V voltage, and the rated current of the fuse is 5A. So, decided to make alternatives: after disassembling the yellow package of D2 diode, it can be seen that it is a spherical high-power low-frequency rectifier diode, retain the original connector plug, and buy an imported spherical high-power rectifier diode (rated current 5A, Rated voltage 500V) soldered to the original connector plug. Self-made diode
After plugging in and running, you can use the key switch to control the start and stop of the engine smoothly.
Failure analysis
The output of this type of excavator generator is a normal 28V voltage, and the load quick-break relay in the circuit works normally (anti-shock voltage protection circuit works normally), so the generator will not produce a surge voltage on electrical components when the engine is stopped; It means that the D2 diode in the line will not be broken down by large current due to short circuit. After analysis, there are two main reasons for the breakdown of the D2 diode: one is working for a long time in a large current environment and causes breakdown; the other is the reverse breakdown voltage degradation causing breakdown. After replacing the self-made diodes, the excavator worked normally for more than a month, indicating that the D2 diode was broken down due to its own aging, and there were no other faults in the line.
