Issue 1, Section 150-231-164
Revision 04
Page 37
TABLE 13. HLU-231 GNLB TEST PROCEDURES
Step
Action
1
Have the CO tester send the HRU-412 (3 in 7) in-band loop-up code for five seconds. Observe that the
HLU-231 List 6D displays the “NREM” message indicating an HRU-412 loopback is in effect (Figure 14).
2
Have the CO tester transmit a T1 test signal into the HLU-231 List 6D and verify that the returned
(looped) signal is error free.
3
If the above test fails, have the CO tester transmit the (3 in 5) in-band loop-down code. Verify that the
HLU-231 List 6D display returns to normal.
4
Have the CO tester send the HLU-231 List 6D (4 in 7) in-band loop-up for five seconds. Observe that
the HLU-231 List 6D displays the “NLOC” message indicating an HLU-231 List 6D loopback is in effect.
5
Repeat Step 2. If the test passes, the problem is in the cable pair or the HRU-412. If it fails, the
problem is in the CO equipment.
6
The NREM and NLOC loopbacks can also be initiated from the front panel of the HLU-231 List 6D with
the MODE and SEL push-buttons (Section C Paragraph 3.10).
7
The HLU-231 List 6D can be looped-up from the remote location (CREM) by issuing the (6 in 7)
command at the HRU-412 DS1 input port.
8
The HRU-412 can be looped-up from the remote location (CLOC) by issuing the (5 in 7) command at
the HRU-412 DS1 input port.
9
Doubler #1 can engage loopback from the remote location (CDU1) by issuing the (4 in 6) loopback
command at the HRU-412 DS1 input port.
10
Doubler #1 can engage loopback from the local location (NDU1) by issuing the (2 in 6) loopback
command at the HLU-231 List 6D DS1 input port.
11
Doubler #2 can engage loopback from the remote location (CDU2) by issuing the (5 in 6) loopback
command at the HRU-412 DS1 input port.
12
Doubler #2 can engage loopback from the local location (NDU2) by issuing the (3 in 6) loopback
command at the HLU-231 List 6D DS1 input port.
Note 1
When T1 loopback tests are performed on the HiGain system with metallic loopback connections at either end,
the DS1 code that occurs at the metallic loopback interface may be different from the DS1 code being received
at the opposite end when the DS1 user code is set to AUTO. For example, if the HRU-412 has a metallic
loopback and the HLU-231 List 6D receive pattern's code is changed from AMI to B8ZS and the all “0” pattern is
sent into the HLU-231 List 6D, the HRU-412 remains in its AMI mode and thus loops all “0”. This causes the
HRU-412 to indicate a LOS condition which then causes the HLU-231 List 6D to output the AIS pattern.
Note 2
The HiGain system may take longer than normal to respond to in-band commands when its framing mode is set
to UNFR and the in-band commands are sent in either an SF or ESF mode. The frame bits override the
command bits and cause errors in the command sequence. These errors cause the HiGain system to reject
some sequences. This can extend the detection interval.
