User manual

Publication 1747-IN011F-EN-P - May 2007
144 Troubleshooting
Tips for Troubleshooting
Your Control System
When troubleshooting, pay careful attention to these general
warnings.
The first step in the troubleshooting procedure is to identify the
problem and its source.
Locate the majority of faults by observing the diagnostic indicators on
the front of the power supply, processor unit, and I/O modules. These
indicators, along with error codes identified in the programming
device user manual and software, help trace the source of the fault to
the user’s input/output devices, wiring, or the controller. Faults which
do not clear by either toggling the keyswitch from Program to Run or
cycling power, cannot be diagnosed or corrected without
programming software.
A flashing fault status indicator may indicate the user program in the
processor is corrupted and a copy of the program will be needed
before contacting your local Allen-Bradley sales office or distributor
for assistance.
Removing Power
Before working on a SLC 500 modular system, always remove the
power supply input power at the main power disconnect switch.
The power status indicator on the power supply indicates that dc
power is being supplied to the chassis. The status indicator could be
off when incoming power is present.
ATTENTION
Have all personnel remain clear of the controller and equipment
when power is applied. The problem may be intermittent and
sudden unexpected machine motion could result in injury. Have
someone ready to operate an emergency-stop switch in case it
becomes necessary to shut off power to the controller
equipment. Also, see NFPA 70E Part II for additional guidelines
for safety-related work practices.
Never reach into a machine to actuate a switch since
unexpected machine motion can occur and cause injury.
Remove all electrical power at the main power disconnect
switches before checking electrical connections or
inputs/outputs causing machine motion.