DEC DECstation 5000 Model 100 Series, Maintenance Manual

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Troubleshooting When a Printer, Modem, or Alternate
Terminal Does Not Operate Properly
If the system tests report no errors, but a printer, modem, or
alternate terminal does not operate properly, run an external
loopback serial line test to isolate the problem.
Before you run the external loopback serial line test, make sure
the following items are installed on the back of the system unit:
Communications loopback connectors on both communica-
tions connectors
A keyboard-mouse cable that has the following attached:
A keyboard attached to the keyboard connector
A mouse or mouse loopback connector attached to the
mouse connector
To run the external loopback serial line test, type
t dz/modem/ [line] [cts-lbk]. Then press Return.
When you type the external loopback test command,
Use the line parameter to specify the serial line you want
to test.
Specify comm to test the communications line that is
on the right as you face the back of the system.
Specify port to test the communications line that is on
the left as you face the back of the system.
Use the cts-lbk parameter to specify the type of test to
run.
Specify n to run a data-leads-only test.
Specify y to run a clear-to-send test.
If the external loopback serial line test reports an error, the
serial line controller is faulty. Replace the system module and
chassis. Refer to ‘‘System Module’’ in Chapter 5 for directions.
If the external loopback serial line test succeeds, the printer or
modem is faulty. Refer to the printer or modem service guide to
troubleshoot.
4–10 Identifying Failed FRUs