5.3.1 Local Analog Loopback (LAL)
The Local Analog Loopback (LAL) test checks the operation of the
local Model 1040, and is performed separately on each unit. Any data
sent to the local Model 1040 in this test mode will be echoed (returned)
back to the user device. For example, characters typed on the
keyboard of a terminal will appear on the terminal screen. To perform a
LAL test, follow these steps:
A. Activate LAL. This may be done in one of two ways: First, by
moving the front panel toggle switch DOWN to “LAL”. Second,
by raising pin 18 on the RS-232 interface (Note: Make sure
DIP switch SW2-8 is OFF). Once LAL is activated, the Model
1040 transmit output is connected to its own receiver. The
“test” LED should be lit.
B. 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.
C. Perform a BER (bit error rate) test on each unit. 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 RS-232
interface cable between the terminal and the Model 1040.
5.3.2 Remote Digital Loopback (RDL)
The Remote Digital Loopback (RDL) test checks the performance
of both the local and remote Model 1040s and the communication link
between them. Any characters sent to the remote Model 1040 in this
test mode will be returned back to the originating device. For example,
characters typed on the keyboard of the local terminal will appear on the
local terminal screen after having been passed to the remote Model
1040 and looped back. To perform an RDL test, follow these steps:
A. Activate RDL. This may be done in two ways: first, by moving
the front panel toggle switch UP to “RDL”. Second, by raising
pin 21 on the RS-232 interface (Note: Make sure SW2-8 is
OFF).
B. Perform a BER (bit error rate) test on the system.
C. If the BER test equipment indicates a fault, and the Local
Analog Loopback test was successful for both Model 1040s,
you may have a problem with the twisted pair line between the
modems. Make sure you check the twisted pair line for proper
connections and continuity.
5.3.3 Using the V.52 BER Test Independently
The V.52 BER test can be used independently of the V.54 loopback
tests. This requires two operators: one to initiate and monitor the test
at the local Model 1040, and one at the remote Model 1040. To use the
V.52 BER test by itself, both operators should simultaneously follow
these steps:
1. Locate the “511/511E” toggle switch on the front panel of the
1040 and move it DOWN. This activates the V.52 BER test
mode and transmits a “511” test pattern to the other unit. If
any errors are present, the receiving modem’s red “Error” LED
will blink sporadically. Note: For this test to function, the “511”
switch on both Model 1040s must be on.
2. If the test indicates no errors are present, move the V.52
toggle switch UP, activating the “511/E” test with periodic
errors present. If the test is working properly, the receiving
modem's red “Error” LED will light continuously. A successful
“511/E” test will confirm that the link is in place, and that the
Model 1040’s built-in “511” generator and detector are working
properly.
5.4 POWER-DOWN
Turn off the Model 1040 by simply removing it from the circuit or by
turning off the terminal that is directly connected to the Model 1040.
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