Patton electronic 1090 - Manual (Page 9)

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 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 1090.
5.3.2 REMOTE DIGITAL LOOPBACK (RDL)
The Remote Digital Loopback (RDL) test checks the performance of
both the local and remote Model 1090', and the communication link
between them. Any characters sent to the remote Model 1090 in this
test mode will be returned back to the originating device.
To perform an RDL test, follow these steps:
A. Activate RDL. 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 RL signal on the terminal interface (for
pin numbers, see Appendix D).
B. Perform a BER (bit error rate) test on the system, using BER
testers on both ends.
C. If the BER test equipment indicates a fault and the Local
Analog Loopback test was successful for both Model 1090s,
you may have a problem with the line between the Model
1090s. You should inspect the line for proper connections.
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5.3.3 LOCAL DIGITAL LOOPBACK (LDL)
The Local Digital Loopback (LDL) test checks the local and remote
1090s and all communication paths. In LDL, the TX/RX circuit of the
local 1090 closes, thereby allowing characters sent from BOTH the
local terminal and remote terminal to loop back (echo) to themselves
(See Figure 8, below). To accurately perform LDL diagnostics,
technicians must send characters (or BER diagnostics) from each end.
To perform a LDL, follow the instructions below:
A. On the bottom of the unit, turn S1-4 to the ON position.
B. Enable LDL by moving the front panel toggle switch up to
“Local”, Or, by raising the signal LL on the terminal
interface(for pin numbers, see Appendix D).
C. Perform a BER (bit error rate) test on the system, using BER
testers on both ends.
D. If the BER test equipment indicates a fault and the Local
Analog Loopback test was successful for both Model 1090s,
you may have a problem with the line between the Model
1090s. You should inspect the line for proper connections.
NOTE: LDL will only work when S1-4 is ON.
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Figure 7. Remote Digital Loop
Figure 8. Local Digital Loop