Black Box MD1641A Manuale Utente

in Figure 8-6), the Local Analog Loopback Test should be performed
on both the remote and local modems. If that test is successful, the
problem may be the phone lines. 

First make certain that you are set up for Synchronous operation by
placing DIP-Switch #12 in the UP position. To initiate the Digital
Loopback Test (remote/automatic), DIP-Switch #9 must be in the
DOWN position, and the Answer/Originate switch (front of the
modem) must be toggled to the UP position. Once you receive an OK
message from your modem (if responses are enabled), the local modem
is placed in Digital Loopback mode. To exit the Digital Loopback Test
(remote/automatic), toggle the front panel Answ/Orig switch to the
Answer position.

Type 

or 

; hit ENTER

Computer or

Terminal

Local Series

II Modem

digital

analog

Computer or

Terminal

digital

analog

Local Series

II Modem