ALLEN BRADLEY 1747-L551 PLC Processor

Troubleshooting
10–27
Troubleshooting Your Input Modules
If your Input
Circuit LED is
On
Off
And Your Input
Device is
On/Closed/Activated
Off/Open/Deactivated
at
On/Closed/Activated
Off/Open/Deactivated
And Probable Cause Recommended Action
Your input device will not turn
off.
Your program operates as
though it is off.
Your program operates as
though it is on and/or the input
circuit will not turn off.
Your program operates as
though it is off and/or the input
circuit cuit will not turn on.
Your input device will not turn
on.
Your program operates as
though it is on.
Device is shorted or
damaged.
Input circuit is
damaged.
Input is forced off in
program.
Input device Off-state
leakage current
exceeds input circuit
specification.
Input device is shorted
or damaged.
Input circuit is
damaged.
Input circuit is
incompatible.
Low voltage across the
input.
Incorrect wiring or an
open circuit.
Input signal turn on
time too fast for input
circuit.
Input circuit is
damaged.
Input device is shorted
or damaged.
Input is forced on in
program.
Input circuit is
damaged.
Verify device operation. Replace device.
Verify proper wiring. Try other input
circuit. Replace module.
Check the FORCED I/O or FORCE LED
on processor and remove forces.
Check device and input circuit
specifications. Use load resistor to
bleed-off current.
Verify device operation. Replace device.
Verify proper wiring. Try other input
circuit. Replace module.
Check specification and sink/source
compatibility (if DC input).
Check the voltage across input circuit
and check source voltage.
Check wiring and COMmon
connections.
Check timing specifications.
Verify proper wiring. Try other input
circuit. Replace module.
Verify operation. Replace device.
Check processor FORCED I/O or
FORCE LED and remove forces. Verify
proper wiring. Try other input circuit.
Replace module.
Verify proper wiring. Try other input
circuit. Replace module.
Publication 1747-6.2