Investigation sequence
Map the input path
Identify disconnect, line fuses, input contactor, EMC/filter section, rectifier and precharge arrangement.
Check charge timing
Document whether bus voltage rises slowly, never rises, rises then collapses, or causes a fuse/precharge component failure.
Inspect switching around precharge
Check precharge relay/contactor command, welded or open contacts, burned resistor and control-supply dependency.
Look for downstream shorts
A shorted inverter bridge, brake chopper or capacitor bank can overload precharge and mislead the diagnosis.
Connect to fault pages
Route to no-display, undervoltage or overvoltage records based on measured evidence rather than panel wording alone.
Stop conditions
- Bus voltage does not discharge predictably
- Input fuse opens repeatedly
- Visible capacitor venting or electrolyte
- Unknown terminal identity
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.