Yaskawa GA500 fault Uv1: DC Bus Undervoltage
Fault Uv1 on a Yaskawa GA500 is DC Bus Undervoltage: the DC bus voltage fell below L2-05 [Undervoltage Detection Lvl] while the drive was running. The level is approximately 190 V for 200 V class drives and 380 V for 400 V class drives (about 350 V when E1-01 is below 400).
Diagnose this with AI
Try Free Drive Diagnostic Upload a keypad photo, the fault history or a parameter export from your Yaskawa GA500. InduQT compares the evidence and suggests the next useful checks.
When it happens
- Running when the supply dips, fails or loses a phase
- Under load on a weak or unstable supply
- Not while stopped; then the drive shows the Uv alarm instead
Likely causes and checks
1Input phase loss
- Points to it
- Trips under load; PF (Input Phase Loss) may also appear.
- Check
- With the drive isolated, check the main circuit input wiring and fuses, then measure all three phases under load.
2Loose input terminals
- Points to it
- Intermittent trips; heat marks on terminals.
- Check
- Tighten the input terminal screws to the specified torque.
3Supply dip, loss or unstable voltage
- Points to it
- Trips coincide with plant power events or large loads starting.
- Check
- Log the input voltage; if the supply is good, check the main circuit magnetic contactor.
4Worn main circuit capacitors
- Points to it
- Older drive; trips with a healthy supply.
- Check
- Read U4-05 [CapacitorMaintenance]; above 90% the manual says to replace the board or drive.
5Damaged soft-charge bypass relay
- Points to it
- Repeated Uv1 with healthy supply; U4-06 high.
- Check
- Read U4-06 [PreChargeRelayMainte]; above 90% replace per the manual.
Telling it apart
- Uv1 (fault, ALM steady) occurs while running. Uv (alarm, ALM flashing) is the same low bus voltage while stopped. Uv2 is control power undervoltage; Uv3 is a soft-charge answerback fault.
- Fault trace (U2-xx) is not available for Uv1, so record the plant supply conditions separately.
- V1000 equivalence: the V1000 manual lists Uv1 (DC Bus Undervoltage) with detection at L2-05, approximately 190 V (160 V for single-phase drives) or 380 V, and notes Uv1 and Uv2 are not saved to the fault history.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| L2-05 | Undervoltage Detection Lvl (Uv1) | Default set by o2-04 drive model and E1-01. |
| U4-05 | CapacitorMaintenance | Main circuit capacitor life; replace above 90% per the manual. |
| U4-06 | PreChargeRelayMainte | Soft-charge bypass relay life. |
| L5-08 | Fault Reset Enable Select Grp2 | Controls whether auto restart applies to Uv1. |
Evidence to collect
- Keypad photo with ALM LED state
- Measured input voltage on all phases, under load
- U4-05 and U4-06 maintenance monitors
- Plant power events at the trip time
- L2-05 and E1-01 settings
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