User manual

2270 Fiber Optic Modem

Step Symptom Possible Cause(s) Action

2 (cont.) Perform the following optical loss calculation:

• Local Receiver level minus remote Transmit level = near-end link loss figure

• Remote Receive level minus local Transmit level = far-end link loss figure

Check the optical cable loss figure against the optical link loss budget specified in

Table 1-B for the specific fiber-optic modem. For the HP Laser version, check that the

Tx PWR and Rs SENS switches are set according to Section 1.10.3.

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.

NOTE: The link loss should be at least 3 dB lower than the loss budget speci-

fied for the modem. This design margin will compensate for LED/Laser aging

and small changes in the actual link loss.

3 Cable loss exceeds Defective F/O cable Repolish or replace

modem loss budget defective connectors

4 Cable loss exceeds Defective F/O connectors Repair or replace

modem loss budget defective cable

5 Set up BERT for the proper clocking, data rate and format as used with the circuit. Use

the existing interface cables if possible. Connect the BERT in place of the local user

device. Connect a data clock loopback connector in place of the remote user device.

Run the BERT test and go to the next step.

6 System loopback test Modem not configured Verify/correct switch and

passes but modems properly strap settings on modem

will not pass data and devices

7 System loopback test Interface cables damage Repair damaged or

passes but modems or miswired miswired cables

will not pass data

Optically loopback each modem and repeat BERT test as detailed in Step 5

8 Modem fails BERT test Defective modem or Replace defective modem

when optically looped electrical interface

back to itself