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15/05/2024

The cargo crane does not slew. Troubleshooting

Greetings! Today we have a problem with the cargo crane, it won’t slew. In this case, there are no signals or alarms, the crane starts up, executes the commands “jib up, hook up” and “jib down, hook down,” but does not slew in any direction.

The cargo crane does not slew. Troubleshooting

According to the instructions for the crane, you need to check the following circuit: Joystick - PLC - relay - Proportional Driver Unit - Proportional Valve.

Let's check the entire electrical circuit and figure out the reason for the improper operation of the cargo crane.

The command given by the operator using the joystick is received by the PLC module, processed, the intermediate relay prepares the circuit, then the command goes to the proportional driver, which sends a signal in milliamps to the proportional valve of the crane rotation hydraulic pump (two solenoids - right and left).

Slewing circut
Slewing circut

I will not go into details of checking the entire circut, because you can read about this in the previous article, where the problem of the slow operation of the cargo crane was described and the remaining elements after the joystick were checked.

Here the problem turned out to be in the joystick, at the very beginning of the circuit. It did not give a signal to the PLC and, accordingly, further along the circuit.

Operation circuit diagram of joystick, driver and valves
Operation circuit diagram of joystick, driver and valves

The circuit diagram shows how the joystick works, using a potentiometer and microswitches it sends a command to the PLC, the 58K relay “informs” that the circuit is ready, and through the 42AMP driver it affects the proportional valves (right and left).

Command from joystick to valve
Command from joystick to valve

Because the circuit beyond the joystick visually did not work, then the problem had to be looked for in the joystick itself. After opening the joystick, one wire broke off, apparently due to poor soldering.

Repair of a joystick for slewing the crane
Repair of a joystick for slewing the crane

The wire was soldered into place, cargo crane was put into operation. For a more detailed study of the operation of the crane, I recommend the previous article.

Crane model: DMC DDKC-3026-00 (Dongnam Marine Crane).

Also read other articles about DMC cargo cranes:

  1. Problems with cargo cranes. Some problems with cargo cranes that occur on the ship
  2. The crane hook goes up slowly. The cargo crane is not working. Troubleshooting
  3. PLC failure. The cargo crane does not start. Troubleshooting
  4. Motor Fault on the crane. Troubleshooting
  5. The crane jib is luffing down under its own weight. Troubleshooting

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