Fault Phenomenon: Foton Raysta L10 boom retracts normally when cold. After reaching operating temperature (oil temp 90℃), the final boom section moves slowly and eventually becomes completely inoperative, with no alarm on the dashboard.

Troubleshooting Process:
– Checked hydraulic line routing: no bends, fittings no leaks.
– Checked multi-way valve spool: control handle signal normal, spool moves smoothly.
– Checked solenoid coil resistance: normal when cold.
– Measured solenoid valve drive current at operating temperature: found current value is only 30% of rated.

Root Cause: Power transistor inside the Boom Control Unit (BCU) suffers thermal breakdown.

Required Parts: Boom control computer board (BCU) assembly.