User manual
Publication 1394-5.0 — May 2000
9-10 Troubleshooting
Understanding Analog Servo 
System Module Faults
The faults that apply to the Analog Servo System’s system module 
appear in the following tables.
Note: Although these faults are for the Analog Servo version, in many 
instances, the descriptions, causes, and resolutions can also 
apply to the GMC version. The fault messages, however, would 
be different. Refer to the GML Programming Manual 
(publication 999-104) for more information.
Fault Message: Description: Potential cause: Possible resolutions:
Bus Config
The configured bus 
voltage mode does not 
match the hardware.
The system module detected an incorrect 
shunt module configuration (wrong shunt 
installed).
• Verify that the shunt module is rated for 
and compatible with your system 
module.
 Custom shunt parameters exceed the system 
module shunt limits.
• Verify custom shunt parameters do not 
exceed the system module limitations.
Bus Low Vlt
The DC power bus 
activates undervoltage 
limit when the bus drops 
to 275V DC or less. It 
will clear at 300V DC.
The voltage on the 360/480V AC input power 
is low.
Verify incoming AC voltage and change 
the supply source, if needed.
Bus Ovr Vlt
The DC Power Bus is 
continuously monitored. 
If it exceeds a preset 
level (810V DC), a fault 
is sensed and the power 
supply is disabled.
Bus Voltage Operation
Shunt turns on at 
800V DC
Shunt turns off at 
750V DC
Over voltage trip point 
810V DC
Under voltage trip point 
275V DC
Under voltage fault 
clears at 300V DC
If this fault occurs when you power up the 
system module with the M-contactor, the 
power distribution impedance might be stiff or 
line voltage might be too high.
• Perform line conditioning.
• Verify that line voltage is within 
specifications.
The position controller acceleration / 
deceleration rate is incorrectly set.
Change the command profile to reduce 
speed or increase time.
The system inertia is too high causing 
excessive energy to be returned to the power 
supply bus.
• Change the command profile to reduce 
speed or increase time.
• Use a larger external shunt resistor.
A vertical axis with insufficient 
counterbalancing is overdriving the servo 
motor and causing excessive energy to be 
returned to the power supply bus.
• Use the external shunt resistor.
• Increase the mechanical 
counter-balance on the machine.
Input line voltage exceeds the maximum input 
voltage rating.
Verify incoming 360/480V AC input 
voltage and change the supply source, if 
needed.
Power Driver Board is malfunctioning and is 
incorrectly sensing the bus voltage.
Replace the system module.
The shunt regulator or transistor has 
malfunctioned.
Replace the system module.
External shunt regulator fuse has blown.
Check and possibly replace the shunt 
resistor.
CAN Hdwr
SCANport hardware 
error detected.
The SCANport device or cable is faulty. 
Check SCANport connections.
Cntctr Flt
Three-phase power is 
either detected when it 
shouldn’t be or not 
detected when it should 
be.
The contactor is welded or failed to open.
• Correct wiring.
• Replace the contactor.
The input wiring to your contactor is incorrect.
Correct wiring.
Cur Limit
The system module has 
reach its current limit.
The motoring/regenerative current produced 
by the motor(s) and axis module(s) exceeds 
the current limit allowed by the system 
module.
• Increase system module size. The sum 
of the axis modules continuous current 
exceeds the system module current 
limit rating.










