Specifications

Loopback Tests 5-1

Chapter 5

Troubleshooting and

Diagnostics

This chapter contains procedures for performing FOM-40 diagnostic tests. Use the

test procedures provided in this chapter to:

• Verify normal system operation

• Isolate faulty equipment

• Identify other sources of system malfunction.

The tests are activated by control pushbuttons on the FOM-40 front panel and

monitored with LED indicators. For a description of FOM-40 controls and

indicators and their functionality, see Chapter 3.

5.1 Loopback Tests

FOM-40 supports several types of loopback tests for evaluating the operation of

the data system equipment and its line circuits. Using these loopbacks, you can

test communication between the attached equipment, and internal circuitry of the

local and remote modems.

Loopback tests are best performed in the following order:

1. Local analog loopback

2. Remote digital loopback

3. Local digital loopback.

Before testing the operation of the data system equipment and line circuits, ensure

that all the units are powered up and configured properly.

If you want to run the LLB and RLB tests via the DTE interface pins, ensure that

switch SW5/5 is set to ON (see Table 2-1 and Figure 2-1). LLB and RLB activation

through the DTE interface pins is not available for the X.21, G.703 and Ethernet

interfaces.

When you send a remote loopback pattern (V.54) through the DTE, the local

FOM-40 unit may go into a digital loopback as well. To avoid this, ensure that

switch SW6/2 on the local modem is set to ON and switch SW6/1 on both units are

set to ON.

Note