Yaskawa GA800 E43 Fault — What It Means
The E43 fault on a Yaskawa GA800 VFD indicates a soft-charge or bypass relay answerback failure. During power-up, the drive expects the soft-charge bypass relay to change state and send back a feedback signal confirming the relay has switched correctly. When the drive does not see the expected relay response, it shuts down and reports E43. This points to a problem in the relay itself, the feedback wiring path, or the control board circuitry that commands and monitors the relay.
The soft-charge circuit is part of the drive’s DC bus pre-charge sequence, which limits inrush current when the drive first energizes. A failed relay, stuck contacts, burned connections, or a control board that can no longer drive or read the relay will all trigger this fault. The GA800 also tracks relay life in parameter U4-06 (PreChargeRelayMainte), and Yaskawa guidance states that when U4-06 exceeds 90%, the relay, board, or drive should be replaced.
Before You Replace Anything
Technicians sometimes replace the entire drive before checking relay life parameter U4-06 or inspecting the relay contacts and wiring for heat damage or loose connections.
Common Causes
- Worn or stuck soft-charge bypass relay Repeated power cycles wear relay contacts until they no longer close or open cleanly, blocking the answerback signal the drive expects.
- Failed control board relay-drive circuit The control board circuitry that energizes the relay or reads its feedback can fail, even when the relay itself is intact.
- Loose or burned relay wiring connections Heat, vibration, or poor torque on terminals in the relay feedback path creates intermittent or open circuits that prevent the drive from seeing the relay state.
- Relay life counter above 90% Parameter U4-06 tracks relay cycles, and Yaskawa troubleshooting guidance recommends replacement when this counter exceeds 90%.
- Damaged board-to-board connectors Internal connectors linking the control board to the relay circuit can crack, corrode, or unseat, breaking the feedback loop.
- Power surge or transient event Lightning, line voltage spikes, or switching transients can damage the relay coil, contacts, or board traces in the soft-charge circuit.
Quick Diagnosis
Answer these to narrow it down fast.
Does the fault appear every time you power the drive, or only once?
No: A one-time E43 can be a transient event. Monitor the drive, but if it does not recur, no repair may be needed.
Is parameter U4-06 (PreChargeRelayMainte) above 90%?
No: The relay life counter is still acceptable. Focus on inspecting physical relay condition, wiring, and connections.
Do you see heat discoloration, arcing marks, or loose terminals on the relay or wiring?
No: No visible damage suggests an internal control-board fault. Replace the control board or consult Yaskawa service for drive replacement.
Step-by-Step Fix
- Disconnect all power and lock out the drive at the upstream disconnect or breaker before opening any covers.
- Wait for DC bus capacitors to discharge per the GA800 manual (typically five minutes minimum), then verify zero voltage with a meter.
- Power the drive back on and observe whether E43 appears immediately or if the drive starts normally. Record whether the fault is repeatable.
- Check parameter U4-06 (PreChargeRelayMainte) on the keypad or software. If the value is above 90%, plan to replace the relay assembly or control board.
- Inspect the soft-charge bypass relay and all associated wiring for loose terminals, heat discoloration, burned contacts, or mechanical damage.
- Test all terminal connections in the relay feedback path with a torque screwdriver to confirm they meet the torque specification in the GA800 manual.
- Replace the control board or relay assembly if physical inspection finds no damage and the fault persists. Yaskawa documentation limits field repair to board and relay-contactor replacement, not component-level fixes.
- Re-energize the drive after any repair, monitor for fault recurrence, and log the repair in your maintenance records.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa GA800 control board (PCB) | Amazon | Order by exact drive model and frame size. Board handles relay drive and answerback feedback. |
| Soft-charge bypass relay or contactor assembly | Amazon | Verify part number from drive nameplate or contact Yaskawa. Not all GA800 frames use the same relay. |
| Replacement terminal lugs or crimp connectors | Amazon | Use if existing relay or board terminals show heat damage or poor contact. |
When to Call a Pro
Call a qualified electrician or VFD service technician for any E43 fault. The soft-charge circuit operates at high DC bus voltage (typically 300-800 VDC depending on input line), and incorrect handling can cause arc flash, electric shock, or permanent drive damage. Technicians need a working knowledge of VFD startup sequences, access to Yaskawa service documentation, and calibrated test equipment to safely diagnose relay feedback paths and control board circuitry. If parameter U4-06 exceeds 90% or physical inspection reveals burned components, the repair requires board or relay assembly replacement that is beyond typical homeowner capability. Yaskawa GA800 service documentation explicitly limits user-serviceable components to fans and control boards, so any deeper troubleshooting should be handled by factory-trained service personnel or an authorized Yaskawa distributor.
Rough cost: A pro service call runs about $300-800 for board or relay assembly replacement, depending on drive size and labor.