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5.3 DIAGNOSTICS
Model 1184 and 1185 are equipped with V.54 diagnostics that may
be used to to evaluate the condition of the local and remote units, as
well as the twisted pair link between them: local loopback (LAL) and
remote digital loopback (DL).
5.3.1 Local Analog Loopback
The Local Analog Loopback (LAL) test checks the operation of the
local Model 1184 or 1185 and is performed separately on each unit.
Any data sent to the local Model 1184/1185 in this test mode will be
echoed (returned) back to the user device. (See Figure 7, below). For
example, characters typed on the keyboard of a terminal will appear on
the terminal screen.
To perform a Local Analog Loopback test, follow these steps.
1. Activate LAL either by moving the front panel toggle switch
DOWN to “Local”, or; by raising the appropriate signal on
the DTE interface. Once Local Analog Loopback is
activated, the Model 1184/1185’s transmit output is connected
to its own receiver. The test LED should glow.
NOTE: Although the local Model 1184/1185 cannot communicate with the remote
Model 1185/1185 in this mode, the synchronized connection between the two
modems remains intact.
2. Verify that the data terminal equipment is operating properly
and can be used for a test. If a fault is indicated, call a
technician or replace the unit.
3. Perform a BER (bit error rate) test on each unit using a
separate BER tester. If the BER test equipment indicates no
faults but the data terminal indicates a fault, follow the
manufacturer's checkout procedures for the data terminal.
Also, check the interface cable between the terminal and the
Model 1184/1185.
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5.3.2 Remote Digital Loopback
The Remote Digital Loopback test checks the performance of both
the local and remote Model 1184/1185,
and
the communication link
between them. Any characters sent to the remote unit in this test mode
will be returned back to the originating device (see Figure 7).
To perform an DL test, follow these steps:
1. Activate DL. This may be done in one of two ways: First, by
moving the front panel toggle switch DOWN to “Remote”. Or,
second, by raising the DL signal on the terminal interface (for
pin numbers, see Appendix D).
2. Perform a BER (bit error rate) test on the system, using BER
testers on both ends.
3. If the BER test equipment indicates a fault and the Local
Analog Loopback test was successful for both Model 1184 or
1185s, you may have a problem with the line between the
units. You should inspect the line for proper connections.
Figure 7. Remote Digital Loop
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Figure 7. Local Analog Loopback
Local Model 1184/1185