IBM 3270 Maintenance Manual page 344

1.
Reconnect both your system and the other
IBM 3270 Personal Computers to their
original coaxial cables.
2. Rerun the Distributed Function
Communications Adapter diagnostic. (if it is
still loaded, just press "Y" to rerun it.)
DID "CONNECTED TO CONTROL UNIT"
APPEAR ON THE SCREEN?
NO
Follow your procedures to report a
problem external to your IBM 3270
Personal Computer.
YES The problem is resolved. Press N, then
enter. This will end the connection test.
October 1984 3-2800-9