Fault Phenomenon: UpRight TB85 telescopic boom aerial work platform after the boom is extended, it automatically and slowly retracts.

Troubleshooting Process:
– Checked hydraulic lock: poor sealing.
– Checked cylinder seals: piston seals failed.
– Checked counterbalance valve: internal leakage.
– Checked system pressure: pressure normal.

Root Cause: The telescoping cylinder piston seals are worn, causing internal leakage.

Required Parts: Telescoping cylinder seal repair kit.