Fault Phenomenon: Palfinger knuckle boom truck crane when unfolding the boom, the hydraulic lock pin at the knuckle cannot automatically retract.

Troubleshooting Process:
– Checked lock cylinder pressure: insufficient pressure.
– Checked mechanical sticking: pin deformed and bent.
– Checked control solenoid valve: spool not energized.
– Straightened pin and replaced control solenoid valve.

Root Cause: The lock pin was mechanically deformed and stuck, combined with a faulty solenoid valve.

Required Parts: Lock pin, solenoid valve.