Fault Phenomenon: Zoomlion ZLJ5430THB boom deploys normally when cold. After reaching operating temperature (ambient temp 40℃), the third boom section jitters and automatically retracts, with no alarm on the dashboard.

Troubleshooting Process:
– Checked counterbalance valve and hydraulic lock: disassembled and cleaned, cone valve sealed well.
– Checked cylinder internal leakage: pressure holding test normal, no internal leakage.
– Checked angle sensor supply voltage: stable, no fluctuation.
– Measured angle sensor signal at operating temperature: found voltage signal jumps at specific angles.

Root Cause: Internal potentiometer of the boom angle sensor is worn, causing poor contact due to thermal expansion.

Required Parts: Third boom section angle sensor assembly.