IBM 3274 User Manual page 121

Procedure 20: 3299, Attached Displays, and
3299-to-Attached-Displays Link Check
This procedure involves swapping a suspected display signal
cable with another known working display signal cable that is
assigned to an active 3299 output port. Never use an
unassigned 3299 output port.
DANGER
Never connect or disconnect device signal
cables during an electrical storm.
Note:
System operation problems can occur during swapping
of display signal cables if the display types are different
or if the screen size or features of the displays are not
the same.
2-46
1. At the
3299,
swap the signal cable of the failing
display with the signal cable of a known working
display.
2. Set the Normal/Test switch to Test, then to Normal,
at both display stations, or turn power off, then on,
and wait up to 2 minutes, whichever is appropriate.
3. Press the RESET key on the failing display, and
retry the operation.