AT&T Network Adapter 25 Installation And Maintenance Manual page 278

6.
If +7 volts are not present, the ADU is not receiving enough power
from the data terminal and must be locally powered.
7.
If the ADU is powered from a local transformer, make sure that a 3-
pair or 2-pair modular cord is connected between the transformer
and the ADU.
8.
Using a 4-pair modular jack breakout
ac voltage between pins 7 and 8 is
about 28 volts for an open circuit.
9.
Even with alternate power, the data terminal needs to deliver at least
3 volts on pin 20 (DTR signal).
10.
Check the data terminal settings that have been administered at the
SAT to be sure that the administered settings match those of the
data terminal. Settings should be for 8 bits, no parity with O in the
parity bit. Check the baud rate settings. Even if the terminal
accommodates autobaud rate, the administered settings must
include the baud rate.
11.
If the data port is administered for "long break" disconnects, check
to be sure that breaks from the terminal are at least 2 seconds. If
they are not, or if the break length cannot be determined, insert a
device with a disconnect button in the line and enter 2-second
b r e a k s .
12.
Check wiring.
13.
If none of the preceding procedures correct the terminal troubles,
change the ADU.
14.
If the problems persist, replace the Data Line CP.
box, check to be sure that the
about 14 volts under load or
4-101