Siemens 6SE70 Precharge and DC-Link Fault Diagnostic Workflow

Before starting

A MASTERDRIVES DC link can retain lethal energy after input isolation. The workflow starts with documentation, not test leads: record full type code, supply/system topology, fault number/value, point in the machine cycle and whether previous repair or parameter work occurred. Do not acknowledge and restart until the failure has been classified.

Determine whether the machine is line-fed AC-AC, a DC-AC inverter on a common bus, or part of a rectifier/regenerative system. The same panel fault cannot be routed correctly without that topology.

Step-by-step diagnostic logic

For F002, examine why the bus fails to establish through precharge: supply connection, protective devices, contactor control/feedback, precharge path and downstream DC-link condition. For F008, determine whether voltage was never established or collapsed during operation; input sag, rectifier/DC feed and shared-bus events become distinct branches. For F006, correlate the bus rise with incoming voltage or energy returned during motion and regeneration.

After safe isolation and verified discharge, physical evidence may include failed fuses, damaged contactor/precharge components, capacitor stress or disturbed bus connections. Each finding must be related back to the operating event before the unit is re-energized.

Validation and commercial routing

A repair is complete only when the corrected unit passes a controlled startup and the machine no longer reproduces the event under the relevant operation. If the problem arises from a common bus or regenerative system, the verification must include the linked drive/system behaviour.

For an inquiry, submit evidence rather than an unsupported part request. A qualified record can be routed toward repair, identified spare needs, control/back-up preservation or modernization where legacy replacement hardware is constrained.

Detailed branch A: fault at initial energization

When the drive faults during initial energization, do not move directly to the motor side. The unit has not proven the energy foundation needed for output operation. Review supply/topology identity, protective devices, contactor or precharge sequence and any recent cabinet modification. Only under qualified safe conditions should internal bus components be inspected.

If this event followed replacement of a module or control assembly, compare type/configuration evidence with the fitted hardware before assuming the new unit is faulty. Misconfiguration can produce apparent precharge failures that parts swapping will not solve.

Detailed branch B: fault during machine operation

If an established system later reports low or high DC-link behaviour, record the exact production event: acceleration, loaded steady operation, stop, descending load, emergency stop or interaction with other axes. The failure path now includes supply sag, regenerative energy and common-bus behaviour rather than only initial precharge components.

For all branches, completion demands a controlled reproduction of the previously failing operating condition without recurrent faults. A bench power-on that never exercises the triggering event does not prove the repair.

What to record after correction

After a DC-link repair, capture the action taken, the precharge or bus evidence that changed, the unit and system topology, repeated startup result and operation under the prior failing condition. A single cleared fault display is an incomplete validation record.

These close-out facts become useful database assets: they can show whether a component-level issue, cabinet sequence, system energy path or modernization constraint was the actual cause. That is the knowledge that exceeds ordinary service listings and justifies building IndustrialDriveData.

• Root cause classification
• Corrective action
• Safe repeated startup result
• Prior trigger-condition test
• Future risk/modernization note