Alarm guide · Siemens · Updated October 2026
Siemens Sinamics F07900 alarm: motor blocked or speed controller at limit
Siemens Sinamics F07900 means the motor is blocked, or the speed controller is at its limit. Look for a jam, a held brake, wrong phase order or a feedback fault.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The drive applied its maximum torque but the motor did not reach the speed. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Mechanical jam or locked brake
- Motor phase order wrong
- Encoder or feedback fault
- Torque limit too low
- Weak motor
Safe first checks
General guidance only. Follow the drive manual and your site's electrical safety rules. Power off, and let the DC bus discharge, before touching connectors.
- Note the exact alarm code and when it appears: at power-up, at start, or under load.
- Power off and turn the shaft by hand if safe: it should turn smoothly.
- Check the motor cable, encoder cable and connectors for damage and loose contacts.
- Check what changed recently: load, speed, settings, cables or a replaced part.
When to send it for repair
If the mechanism is free, bench test the motor and encoder.
We test every motor on our Universal Servo Motor Repair Equipment, which reads and aligns the feedback and runs the motor under load without the original drive.
See Siemens servo motor repair, Siemens encoder repair and Siemens servo drive repair.
Questions
Is F07900 a drive fault?
Usually it is the mechanism, wiring or the motor feedback.
How long does repair take?
Emergency repair is done the same day where the fault and parts allow, urgent in 3 working days and standard in 7 working days, counted from when the unit reaches our bench and the quote is approved. Every unit returns with a printed test report.
Can I get an exchange unit?
If we hold a matching unit, Servo Swap ships a tested exchange unit while yours is repaired. Mark "line down" on the request form and add the part number.
Related: servo encoder alarms
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.