Danfoss VLT Series Service Manual page 17

SYMPTOM/CAUSE CHARTS
SYMPTOM/CAUSE charts are generally directed towards the more experienced technician. The intent of these charts is to
provide a range of possible causes for a specific symptom. In doing so, these charts provide a direction, but with limited
instruction.
SYMPTOM
1. Control Card Display Is Not Lit.
2. Blown Input Line Fuses
3. Motor Operation Unstable
(Speed Fluctuating)
4. Motor Draws High Current But
Cannot Start. (May appear to rock
back and forth.)
POSSIBLE CAUSES
Incorrect or missing input voltage
Incorrect or missing DC bus voltage
Remote control wiring loading the power supply
Defective Control Card
Defective Interface/ILD Card
Defective Relay Card
Defective or disconnected ribbon cables
Shorted Rectifier module
Shorted IGBT
Shorted DC Bus
Shorted brake IGBT
Mis-wired Dynamic Brake option
Start compensation set too high
Slip Compensation set too high
Improper current feedback
PID Regulator or Auxiliary Reference mis-adjusted
Control signal noise
Start voltage set too high
Open winding in motor
Open connection to motor
One inverter phase missing. Test output phase balance.
Section Two
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