Troubleshooting/Service
Procedure #8
Table 7-11 explains how to troubleshoot a RS 485 Communications failure.
Table 7-12 Troubleshooting a RS-485 Communications Failure
Step What to do How to do it
1
Check the Address Number,
ComState and Baud Rate settings.
See Section 3.13.
Check the field wiring and
termination resistor.
Using an ohm meter, check the resistance across
the communications rear terminals. See Section
2.7 for wiring diagrams.
3
Make sure the Communications
Printed Wiring Board is installed
properly in the controller.
Withdraw the chassis from the case and inspect the
board. See the exploded view (F ) for
location of the board. Return the chassis to the
case.
4
Determine if the Communications
board is faulty by running a LOCAL
LOOPBACK TEST.
If the test fails, replace the board.
If the test passes, the problem is
most likely elsewhere in the
communications network.
Disconnect the communications cable from the rear
terminals. Run the Local Loopback Test.
Press [SET UP] until you see:
COM
Lower Display
SET UP
Upper Display
Press [FUNCTION] until you see:
LOOPBACK
Lower Display
DISABLE
Upper Display
Press
or you will see:
LOOPBACK
Lower Display
ENABLE
Upper Display
The test will run until the operator disables it here.
2
igure 8-1
12/04 UDC3200 Universal Digital Controller Product Manual 167
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