12 7511-A2-GN10-10
January 1999
Troubleshooting

If the 7511 Dual DSU does not turn on the OK LED after its power-up self-test,

refer to the following table.

Symptom Possible Cause Recommendations

No power, or LEDs
are not solidly lit. The power supply to the
carrier has failed.
The card is not seated
properly.
If other devices in the carrier are
functioning, ensure that the card is
completely seated in the rear
connector plate and that the
connector plate is tightly fastened to
the carrier backplane.
Power-up self-test
fails. Only the Alarm
LEDs are on after
power-up.
The DSU has detected an
internal hardware failure. Reset the card by pulling it
slightly out of the carrier then
replacing it.
Contact your service
representative.
An Alarm LED is on. DDS Mode:
The subscriber loop
rate is not matched to
the 7511’s configured
rate.
No DDS Signal
Verify the subscriber loop rate.
If the NS LED is lit:
– Verify that the DSU is
connected to the network
– Request a CSU loopback from
your network service provider
LADS mode:
The 7511 configured rate
does not match its
partner’s rate.
Configure both units to the same
rate.
Crossed pair connection.
(LADS mode only: If the RX
leads are connected to
each other, the NS LED
also will be on.)
Check interface connections and
cable.
One of several other alarm
conditions exists:
Out of Service
Out of Frame
Bit errors detected
during loopback test
(which also causes an
Out of Frame condition)
If the OOS LED is lit:
– Check the status of the remote
DSU
– Initiate a Remote Loopback
Try a different DSU with the
same network connection. If the
problem persists, contact your
service representative.