Yaskawa Sigma-7 A.100 at servo ON, even unloaded: what to check first?
My Yaskawa Sigma-7 SERVOPACK is throwing an A.100 alarm immediately when I try to turn the servo ON, even with no load connected. What should I be checking first to troubleshoot this?
Alarm A.100 on a Yaskawa Σ-7 SERVOPACK indicates an overcurrent has flowed through the power transistor or the heat sink has overheated. This is a Gr.1 alarm and cannot be cleared with a simple reset. When it occurs immediately at servo ON, even unloaded, it strongly suggests a short or ground fault in the main circuit cable, motor, or SERVOPACK itself.
Likely causes and checks
1Main circuit cable miswired, loose, short-circuited or ground-faulted
- Points to it
- This is the most common cause when the alarm trips instantly at servo ON, even without a load. A fault in the cable can lead to an immediate overcurrent condition.
- Check
- With power isolated and the bus discharged, visually check the main circuit cable wiring for correct connections and tightness. Then, use a multimeter to check for short circuits between phases U, V, W, and between each phase and ground on the cable.
2Short circuit or ground fault inside the Servomotor
- Points to it
- If the cable tests good, the next most likely culprit for an immediate A.100 alarm is an internal short or ground fault within the servomotor itself, potentially due to coolant ingress.
- Check
- Disconnect the servomotor from the SERVOPACK. Test for short circuits between U, V, W phases and between each phase and ground at the motor terminals. Replace the motor if it tests faulty.
3Short circuit or ground fault inside the SERVOPACK
- Points to it
- If both the cable and motor test good, the SERVOPACK itself could have an internal short or ground fault, causing the overcurrent alarm even without an external load.
- Check
- With the motor disconnected, check for short circuits across the SERVOPACK's U, V, W output terminals and between these terminals and ground. If a fault is detected, the SERVOPACK should be replaced.
4Regenerative resistor wiring, capacity or resistance problem
- Points to it
- While less likely to cause an immediate trip at servo ON, issues with the regenerative resistor can lead to overcurrent conditions, especially during deceleration of large loads. However, the immediate trip at servo ON points away from this as the primary cause.
- Check
- Check the regenerative resistor wiring for correct connections and integrity. Review the regenerative load ratio in SigmaWin+ and ensure the resistance value is not below the SERVOPACK's minimum allowable value.
Next check: Given the immediate trip at servo ON, start by thoroughly inspecting and testing the main circuit cable for any miswiring, loose connections, short circuits, or ground faults. This is the most common and easiest point to check first.
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