Scope of this technical record
Workflow for undervoltage, precharge, blown-input-fuse or no-display cases where DC-link charging is uncertain.
DC-link service requires rated meters, discharge verification and qualified procedures. Never bypass precharge as a shortcut.
Workflow goal
The workflow identifies whether the DC link is not charging, charging too slowly, charging then collapsing, or charging correctly while feedback/control misreports the condition. Each outcome points to a different repair boundary.
Precharge decision sequence
The sequence reduces false conclusions from a single bus reading.
Precharge workflow matrix
| Stage | Evidence | Boundary |
|---|---|---|
| Input | Supply at drive terminals and fuses | External or input protection |
| Rectifier | Bus begins to rise | Rectifier and DC path |
| Precharge | Controlled charge before main contact | Resistor/relay/contactor |
| Load | Bus collapses or fuse opens | Capacitor/chopper/inverter short |
| Feedback | Measured bus disagrees with display | Voltage sensing path |
Field record checklist
- Input voltage class
- Fuse state
- Charge timing
- Relay/contactor state
- Capacitor/chopper/inverter condition
- Bus feedback evidence
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Circuit path used by this workflow.
Linked records
The symptom belongs to the input, DC-link, precharge and auxiliary control-power boundary until proven otherwise; a dark display is not proof that the keypad itself failed.
The motor is returning energy to the DC link faster than the drive can absorb, dissipate or return it; root cause may be ramp settings, braking hardware, DC-bus feedback or machine load inertia.
Routes incoming three-phase supply through protection, rectification, precharge and DC-link storage before the inverter stage is allowed to run.
Turn this record into a qualified service request
A repair decision is much more reliable when the request includes the exact identity of the drive, the first fault evidence and the machine condition when the symptom appeared.
- Complete drive type code / MLFB or nameplate model
- Fault code, fault value and first event before reset
- When the event appears: power-up, enable, ramp, run, decel or stop
- Motor/cable connected or isolated during the symptom
- Visible board, option-card, module and connector identifiers
- Previous repair history, replacement parts and repeat-failure pattern