Fault Phenomenon: Zoomlion ZR500 rotary drilling rig when operating mast back tilt, it does not stop automatically after exceeding the safe angle, posing a tip-over risk.

Troubleshooting Process:
– Checked angle sensor: back tilt limit sensor failed.
– Checked control system: safety limit logic bypassed or faulty.
– Checked wiring: sensor wiring open circuit.
– Checked mechanical stop: mechanical limit stop missing or deformed.

Root Cause: The mast back tilt angle sensor has severe zero-point drift, causing the system to misjudge the actual angle as smaller, failing to trigger the limit protection.

Required Parts: Replace mast angle sensor and recalibrate.