Investigation sequence
Confirm incoming supply at the drive
Measure at the drive input boundary under site procedure, then inspect upstream fuses, disconnects and contactor evidence.
Establish DC-link charging evidence
Use the correct DC bus terminals or service points for the model. A missing bus points toward input, rectifier or precharge, not keypad failure.
Inspect precharge and auxiliary supply boundary
Look for precharge resistor damage, relay/contactor behavior, SMPS startup components, burned resistors, swollen electrolytics or pulsing low-voltage rails.
Separate supply failure from load short
A collapsed 24 V or 5 V rail may be caused by a downstream fan, I/O, control-board or driver-supply load rather than the regulator alone.
Collect repair evidence
Photograph labels, board identifiers and damaged areas. Decide repair, donor board or drive replacement only after the supply path is proven.
Stop conditions
- Unknown input voltage class
- DC-link cannot be safely verified
- Visible arc or carbonization near power supply
- No qualified isolation equipment
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.
Maps the auxiliary supply route that powers the CPU, keypad, I/O, relay logic, fan control and often isolated driver supplies.
Routes incoming three-phase supply through protection, rectification, precharge and DC-link storage before the inverter stage is allowed to run.