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150-419-100-03>
If trouble is encountered at the T1 interface, verify that the unit is making a
positive connection with the mounting assembly connector.
1
Press the loopback LB button on the HRU front panel for at least five
seconds.
2
Verify that the Green HRU front panel loopback LB NET LED turns on,
indicating that the HRU is in its digital (NREM) loopback state. Also
verify, if possible, that the HLU displays the message NREM also
indicating that the HRU is in loopback (see
3
Have the CO tester transmit a T1 test signal into the HLU and measure
that the returned (looped) signal is error free.
4
If the above test fails, remove the HRU from its loopback state by again
depressing the HRU loopback button for five seconds. Verify that the
loopback NET LED is off.
5
Have the CO tester send the HLU (4-in 7-) in-band loop-up (NLOC) for
five seconds. Verify that the HLU displays the message "NLOC"
indicating that the HLU unit is in its network loopback state.
6
If the test passes, the problem is in the cable pair or the HRU. If it fails,
the problem is at the CO.
7
If the I-CPE 60 mA current option is set to 60 mA, insert an ammeter in
series with the T (Tip) and R (Ring) of either of the two DS1 pairs.
Terminate these pairs with an external NID set to line power and verify
that 30 mA current is flowing.
8
If the sealing current option is enabled (JP1 connected), insert a
milliameter in service with the T or R of either HDSL pair and verify that
at least 20 mA of sealing current is flowing.
When T1 loopback tests are performed using external metallic
loopback connections at either end, the DS1 code that exists
at the metallic loopback interface may be different from the
DS1 code being received at the opposite end when the DS1
user option is set to AUTO.
For example, if the HRU has a metallic loopback, and the HLUs
receive pattern code is changed from AMI to B8ZS, and then
the all 0 pattern is sent into the HLU, the HRU remains in its
AMI mode and thus loops all 0s. This causes the HRU to
indicate a LOS condition which then causes the HLU to output
the AIS pattern.
HRU-419 List 1
September 25, 1998
Figure
21).
Loopbacks
47
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