User's Manual

CHAPTER 6: Troubleshooting

6.5 Remote Digital Loopback

Activate the remote digital loopback test by pressing the REM button or by raising

the level of the remote loopback signal received by the line driver’s V.35 connector

(Pin HH). This test involves creating an outbound loopback at the remote line

driver (see Figure 6-5 on the next page). The test checks the performance of the

local and remote units and the line between them:

1. Press REM or raise remote loopback; the local line driver will signal the

remote unit to start remote digital loopback. The TEST LED should light on

both units. The remote line driver’s receive input should be connected to its

own transmitter.

2. Perform a Bit Error Rate Test (BERT). Either:

• Hook up an external Bit Error Rate Test (BERT) unit in place of the local

DTE; or

• Use the local line driver’s internal BERT. Press the PATT button. The ERR

LED should light briefly just to confirm that the LED is working, and then the

test will proceed. If errors are detected, the ERR LED will be continuously lit

(if the errors are continuous) or will blink (for intermittent errors).

3. If the BERT test indicates a fault, but both line drivers pass their modem self-

tests, there is a problem somewhere in the communication line between the

units.

4. After the test is complete or the fault has been corrected, restore the REM

button to its normal position. Proceed with local digital loopback.