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4.4.2 Removal and Installation 
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Before removing or installing a module, verify that the DC 
power is turned off. 
Removing the Line Interface Unit 
To remove the Line Interface Unit from the RTU proceed as follows: 
1.  Turn off the DC power. 
2.  Disconnect the Line Interface Unit connections. 
3.  Remove the module by pressing the side snaps and lifting the module out. 
Installing a Line Interface Unit 
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If you are installing a new Line Interface Unit, remove it from the 
plastic cover and install the bare board in its place in the RTU housing. 
To install a Line Interface Unit in the RTU proceed as follows: 
1.  Turn off the DC power 
2.  Place the module on the top of the multi-slot I/O card cage. Press down until 
the snaps click into place. 
3.  Reconnect the Line Interface Unit connections. 
4.4.3 Diagnostic LED’s 
The LED indications of the Line Interface Unit are described: 
Telephone Line Option 
OFF HOOK – Indicates that the modem is in off-hook state (lit). 
RING – Indicates an incoming call ring (lit). 
Multi-Drop Option 
TX – Indicates transmission from the modem (lit).