Troubleshooting
According to the electrical system diagram and cab electrical wiring diagram of this excavator, D2 diode and several other diodes are connected in their respective relevant lines in the form of connectors. Disassemble the rear panel of the cab and find three bundled yellow encapsulated diode connectors in the intricate harness. Check the connector connecting wire color and determine the D2 diode by comparing the connecting wire color (RB and RW) of D2 diode identified on the electrical wiring diagram. It can also be determined by removing the D2 diode and observing whether the battery relay cannot be closed when the engine is not started. Remove the D2 diode from the connector socket and measure it with a multimeter. It is found that the resistance in both directions is 0q (see Figure 2), indicating that the D2 diode has been broken down.
Verify the fault point: start the engine, turn off the key switch, and the engine cannot be shut down normally; Unplug the D2 diode, turn off the key switch, and the engine will shut down normally. Prove correct judgment.
The fault point was found, but there was an embarrassment that we couldn't buy parts (the detailed information of D2 diode is not available in the parts atlas provided with the car). Analyze the working conditions of the diode: in the line, D2 diode is mainly used to isolate the reverse DC 24V voltage and the rated current of fuse 5A. Therefore, it was decided to make a self-made substitute: after dismantling 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 in the electronic component market (rated current 5A, rated voltage 500V) welded to the original connector plug. Plug in the self-made diode and test run. The key switch can be used to control the engine start and stop. The instrument also displays normally and the fault is eliminated.
Failure cause analysis
The generator output of this excavator is normal 28V voltage, and the load quick break relay in the circuit works normally (the anti impulse voltage protection circuit works normally) Therefore, when the engine is shut down, the generator will not produce impulse voltage to electrical components; the battery relay works normally, indicating that D2 diode in the line will not be broken down by high current due to short circuit. After analysis, there are two main reasons for D2 diode breakdown: one is that D2 diode is broken down due to working in high current environment for a long time; the other is that reverse withstand voltage degradation leads to being struck After replacing the self-made diode, the excavator worked normally for more than a month, indicating that the breakdown of D2 diode was caused by its own aging, and there were no other faults in the line.
