8.4.71 ALARM 74, PTC Thermistor
Cause
The PTC is not working. Alarm is related to VLT
®
PTC Thermistor Card MCB 112.
8.4.72 ALARM 75, Illegal Profile Sel.
Cause
Do not write the parameter value while the motor is running.
Troubleshooting
• Stop the motor before writing the MCO profile to parameter 8-10 Control Word Profile.
8.4.73 Warning 76, Power Unit Setup
Cause
The required number of power units do not match the detected number of active power units.
Troubleshooting
• When replacing an F-frame module, this will occur if the power specific data in the module power card does not match the rest of
the drive. Confirm the spare part and its power card are the correct part number.
8.4.74 WARNING 77, Reduced Power Mode
Cause
The drive is operating in reduced power mode (less than allowed number of inverter sections). The warning is generated on power
cycle when the drive is set to run with fewer inverters and remains on.
8.4.75 ALARM 78, Tracking Error
Cause
The difference between setpoint value and actual value exceeds the value in parameter 4-35 Tracking Error.
Troubleshooting
• Disable the function or select an alarm/warning in parameter 4-34 Tracking Error Function.
• Investigate the mechanics around the load and motor. Check feedback connections from motor encoder to drive.
• Select motor feedback function in parameter 4-30 Motor Feedback Loss Function.
• Adjust the tracking error band in parameter 4-35 Tracking Error and parameter 4-37 Tracking Error Ramping.
Maintenance, Diagnostics, and
Troubleshooting
Operating Guide | VLT® Refrigeration Drive FC 103
AQ275652766279en-000101 / 130R0707
118 | Danfoss A/S © 2020.01
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