Specifications

Chapter 5 Troubleshooting and Diagnostics FOM-40 Installation and Operation Manual
5-2 Loopback Tests
Local Analog Loopback (LLB)
The local analog loopback (LLB) test checks the performance of the local FOM-40
modem, the local DTE, and the connections between them (see Figure 5-1). The
test is performed separately at the local and the remote site.
FOM-40
Line
Interface
DTE
Transmit
Receive
Data
Clock
Clock
Data
ANA
Pressed
Figure 5-1. Local Analog Loopback

To perform the local analog loopback test:
1. Press the ANA pushbutton.
The TEST LED on the FOM-40 front panel lights up. The modem's transmit
output is now connected to its own receiver.
2. Execute the local analog loopback with one of the following methods:
 Configure the DTE to half-duplex operation and check the echoed data
stream.
 Use an external BER tester to perform a BER test.
If the BER test indicates an error-free data stream, but the DTE test indicates
a fault, check that the cable between the DTE and FOM-40 is properly
connected. If the problem persists, follow the DTE manufacturer's test
procedures.
3. To isolate a communication line problem, perform the LLB loopback at the
opposite end. If both LLB tests are error-free, the fault is probably in the
communication line or in the line interfaces.
4. After completing the test or correcting the fault, press ANA pushbutton again
to restore it to the OFF position.