Fault Phenomenon: Hongda HBT90 distributing boom functions normally when cold. When the boom is fully extended (operating temperature), the boom jitters, positioning is inaccurate, and eventually becomes uncontrollable.

Troubleshooting Process:
– Checked boom counterbalance valve: spool not stuck, good sealing.
– Checked boom cylinder: no internal leakage, piston rod not bent.
– Checked boom controller: output signal stable when cold.
– Measured boom controller output at operating temperature: found output signal drifts.

Root Cause: Thermal drift of the operational amplifier inside the distributing boom controller.

Required Parts: Distributing boom controller assembly.