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Servo overload alarm

Technical review pending. This guide is based on the cited manufacturer documentation; check it against the manual for your exact model and firmware before acting.

A servo overload alarm means the drive’s thermal model of the motor or amplifier says it has been working too hard. Short, very high overloads usually come from a jam, collision, dragging brake or wiring fault; slow, continuous overloads come from the duty cycle, friction or holding a load at standstill. When it trips, and whether a warning came first, tells you which.

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Where it shows up

Likely causes and how to tell them apart

1Brake not released or mechanism jammed

Points to it
Trips quickly from the first move; motor speed does not follow the command.
Check
Confirm the holding brake releases, then turn the mechanism by hand with power isolated.

2Motor power wiring wrong or open phase

Points to it
Trips right after wiring work; motor growls.
Check
Check U/V/W phase order and connections at drive and motor.

3Collision or torque saturation

Points to it
Short-time overload (A.710, AL.51) at the same position each time.
Check
Check for collisions and the peak torque against the motor limit.

4Duty cycle too demanding

Points to it
Continuous overload (A.720, AL.50, S07) after running a while; warnings before the alarm.
Check
Compare effective (RMS) torque over the cycle with the motor continuous rating; lengthen accel/decel or reduce speed.

5Rising friction or holding load

Points to it
Torque at constant speed or at standstill has crept up.
Check
Trend torque over weeks; check lubrication, alignment, bearings and counterbalance.

6Resonance or hunting

Points to it
Overload while stopped with audible hum (MR-J4 AL.50.4).
Check
Check for hunting in servo-lock and retune.

Diagnostic sequence

  1. Read the code and detailInstantaneous vs continuous, running vs stopped (MR-J4 50.1 vs 50.4) narrows the search immediately.
  2. Look for warnings firstAn overload warning before the alarm means heat built up over time; no warning points to a sudden jam.
  3. Check brake and wiringRule out a dragging brake or a wiring fault before changing the profile.
  4. Measure torqueTrend torque over a full cycle and compare RMS torque with the motor rating.
  5. Let it coolMitsubishi asks for about 30 minutes of cooling after an overload alarm; do not reset repeatedly.

Evidence to collect

Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.

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