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3920-A2-GK41-60
February 2002
Removing and Replacing the Model 3920Plus Modem
To remove and replace the Model 3920Plus modem, perform the following steps:
1. Make sure the modem is offline. Press the modem’s back panel power switch to OFF.
2. Disconnect the power cord from the ac power outlet.
3. Disconnect the dc power cable from the connector on the back of the modem.
4. Disconnect the leased-line and dial modular cord(s) from the modem’s back panel.
5. Disconnect the DTE interface cable(s) from the modem’s back panel.
If the modem is to be removed for service, return it to the company using the procedures described in the
Government Requirements and Equipment Return section.
6. Install the replacement modem as described in the Model 3920Plus Modem Installation section, and
configure it the same way as the modem being replaced.
Model 3921Plus Modem Installation
CAUTION
When removing the Model 3921Plus from the carrier, always
use a ground strap when handling the modem. Always store
the Model 3921Plus in an antistatic bag when it is removed
from the carrier.
The 3921Plus modems are designed for installation in a COMSPHERE 3000 Series Carrier, which supplies both
the operating power and the leased and/or dial network connections. For additional information about the
COMSPHERE 3000 Series Carrier, refer to the COMSPHERE 3000 Series Carrier, Installation Manual,
Document No. 3000-A2-GA31.
The COMSPHERE 3000 Series Carrier has 17 slots that holds up to 8 Model 3921Plus multiport modems or
16 Model 3921Plus singleport modems, and one shared diagnostic unit (SDU). The SDU is required when the
modems in the carrier are controlled by an NMS, or when multiple carriers in a cabinet configuration are to be
controlled by a single shared diagnostic control panel (SDCP). The SDCP of the COMSPHERE 3000 Series
Carrier is the user interface to the Model 3921Plus modem. A single SDCP can control up to eight carriers.
