291
Input Units
Symptom
Possible cause
Correction
All inputs do not turn ON, and
i di
t
d
t li ht
External input voltage is not supplied.
Supply power.
p
indicators do not light.
External input voltage is low.
Raise supply voltage.
Terminal screws are loose.
Tighten terminal screws.
Faulty contact of terminal block
connector
Replace terminal block connector.
All inputs do not turn ON, but
indicators are lit.
Input circuit is defective.
Replace defective Input Unit.
All inputs do not turn OFF.
Input circuit is defective.
Replace defective Input Unit.
One input point does not turn ON.
Input device is defective.
Replace input device.
p
p
Input wiring is broken.
Check and replace input wiring.
Terminal screws are loose.
Tighten terminal screws.
Faulty contact of terminal block
connector
Replace terminal block connector.
Input ON-time is too short.
Adjust field input device.
Input circuit is defective.
Replace defective Input Unit.
Input bit is incorrectly programmed in
OUTPUT instruction.
Correct the program.
One input point does not turn OFF.
Input circuit is defective.
Replace defective Input Unit.
p
p
Input bit is incorrectly programmed in
OUTPUT instruction.
Correct the program.
Inputs turn ON and OFF irregularly.
External input voltage is low.
Raise external voltage.
p
g
y
Malfunction due to noise
Countermeasures against noise:
Install surge suppressor.
Install insulating transformer.
Wire with shielded cable.
Terminal screws are loose.
Tighten terminal screws.
Inputs turn ON and OFF irregularly.
Faulty contact of terminal block
connector
Replace terminal block connector.
Abnormal input numbers are in groups
f 8 bit
Common terminal screws are loose.
Tighten common terminal screws.
p
g
p
of 8 bits.
Faulty contact of terminal block
connector
Replace terminal block connector.
Data bus is faulty.
Replace defective Unit.
CPU is defective.
Replace CPU.
Input operation indicator does not
light.
Indicator is defective.
Replace defective Unit.
Troubleshooting
Section 8-6