Fault Phenomenon: Demag chain hoist pressing the button, the motor makes a “humming” sound but does not turn.

Troubleshooting Process:
– Checked voltage: normal.
– Checked brake disc: brake disc rusted, not releasing.
– Checked rectifier: rectifier shorted, DC supply failed.
– Derusted brake disc, replaced rectifier.

Root Cause: The brake motor rectifier shorted, preventing DC power to the brake coil, so the brake did not release.

Required Parts: Rectifier, brake disc.