CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 88)

2240 Fiber Optic Modem User Manual Chapter 6 Diagnostic Procedures
Loopback Test Diagnostic Procedure
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6.2 Loopback Test Diagnostic Procedure
Step Symptom Possible Cause(s) Action
1 No Sync Indication. Defective fiber optic
modem(s), cable(s) or
connectors. If the modems are
configured for a tail circuit (one
is externally locked and the
other is slave), verify that the
externally locked 2240 has a
clock on its TT (or equivalent)
leads that matches its rate
switch. Continue to the next step.
2 Verify the optical cable loss. Remove the Tx fiber from the modem. Use the optical power meter
and fiber optic jumper cable to determine the optical launch power for this modem. Reconnect the
Tx fiber to the modem. Remove the Rx fiber from the modem and determine the optical receive
power into this modem. Reconnect the Rx fiber to the modem. Repeat the above step for the
modem at the other end and record both optical power levels.
Perform the following optical loss calculation:
Near-end Receiver level minus far-end Transmit level = Near-end link loss figure.
Far-end Receiver level minus near-end Transmit level = Far-end link loss figure.
If the optical cable loss figure exceeds the optical link loss budget specified for the modem, set the
optical launch power for the modem(s) to the high power setting and repeat the power
measurements (refer to Chapter 7, "Specifications", for appropriate loss budget figures). If the
actual cable loss still exceeds the loss budget for the modem, go to Step 3. If the cable loss is
within the specified loss budget for the modem, go to Step 5.
3 Cable loss exceeds modem
loss budget. Defective F/O cable Repair or replace defective
cable
4 Cable loss exceeds modem
loss budget. Defective Fiber Optic
Connectors Repolish or replace defective
connector.
5 Set the Remote Loopback switch on the near-end modem. Set up BERT tester for the proper
clocking, data rate and format as used with the circuit. Use the existing interface cables if possible.
Connect the BERT tester in place of the near-end user device. Run the BERT test and go to the
next step.
6 Loopback test passes but
modems will not pass data. Modem not configured
properly. Verify/correct switch and strap
settings on modem and
devices.
7 Loopback test passes but
modems will not pass data. Interface cables damaged or
miswired. Repair damaged or miswired
cables.
8 Optically loopback each modem
and repeat BERT test as
detailed in Step 5 of this
procedure. Modem fails BERT
test when optically looped back
to itself. Defective modem or electrical
interface. Replace defective modem.