IBM 3270 Maintenance Manual page 343

CAUTION
Do not connect or disconnect the coaxial
cable during an electrical storm.
1. Disconnect the coaxial cable from your
system unit. .
2. Disconnect the coaxial cable from one of the
properly functioning units and connect it to
your system unit.
3. Press "Y" then Enter to repeat the connection
test.
DID "CONNECTED TO CONTROL UNIT"
APPEAR ON THE SCREEN?
NO
Reconnect both your system unit and the
other personal computers to their original
coaxial cables. Replace the Distributed
Function Communications Adapter. See
Section 5, "Removal/Replacement and
Adjustments. "
YES
3-2800-8 Maintenance Information