AT&T MERLIN LEGEND Communications System Release 2.0 Maintenance And Troubleshooting Manual page 116

Control Unit Problems
Persistent Module Problems
If any of the module tests fail and replacing the module does not clear the
trouble, one of the following could be the cause:
Several modules could be faulty.
The connector on the carrier could be faulty.
Busy-Out and Reset
Before running any module test, be sure to busy-out or reset the module. This
procedure discontinues service from the module that you are about to test.
The Busy-Out procedure is preferred because it does not drop calls in
progress:
Busy-out discontinues service from the module being tested to each
line and extension only as they become idle. Busy-out does not
disrupt calls in progress.
Reset discontinues service to all equipment instantly. All in-progress
calls are dropped.
Once you complete module testing, restore it as described later in this section
under "Restore." Restoring a module terminates the busy-out or reset
condition.
4-26 Module Problems