NEC FA Series Installation And Maintenance Manual page 104

Backup
Select the Screen Connection tab.
Configure the connection in the same way as for Main (Primary).
* The direction of connection is the same as for Main (Primary).
Next, select the Sending Card tab.
Go to "Redundancy", select the checkbox for "Set as Backup" and click "Save".
Check the current brightness setting.
Click the "Brightness" button.
In the Brightness Adjustment screen, set the desired brightness value and click the "Save to HW" button.
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