Comtech EF Data RCF6001 - Manual (Page 39)

RCF6001 Satellite Terminal Maintenance
TM082 - Rev. 1.0 Page 4-19
Section 4 - Maintenance
4.0 Periodic Maintenance
The DMD2401 LB/ST L-Band satellite modem requires no periodic field maintenance procedures. The unit
contains very few adjustments and most calibration is digital and held in EEPROM. Should a unit be
suspected of a defect in field operations after all interface signals are verified, the proper procedure is to
replace the unit with another known working modem. If this does not cure the problem, faulty wiring,
cabling or power should be suspected.
There is no external fuse on the DMD2401 LB/ST modem. The fuse is located on the power supply
assembly inside the case, and replacement is not intended in the field.
4.1 2401 LB/ST Troubleshooting
The following is a brief list of possible problems that could be caused by failures of the modem or by
improper setup and configuration for the type of service. The list is arranged by possible symptoms
exhibited by the modem.
Symptom: The Modem will not acquire the incoming carrier:
Possible Cause: Improper receive input to modem.
Action: Check that the receive cabling is correct.
Possible Cause: Receive carrier level too low.
Action: Check that the receive cabling is correct, that the downconverter is properly set and that the
LNA is turned on. If a spectrum analyzer is available, locate and measure the receive level, which should
not be below -55 dBm absolute.
Possible Cause: Receive carrier frequency outside of acquisition range.
Action: Check that the receive acquisition range is adequate for the possible system offsets. Setting the
value to 30 KHz is a standard value encompassing all normal offsets. After acquisition, the actual
receive frequency can be read from the front panel.
Possible Cause: Transmit carrier incompatible.
Action: Check the receive parameter settings and ensure that they match those on the modulator.
Possible Cause: Modem is in test mode.
Action: Check the modem front panel for yellow warning LEDs indicating a test mode is enabled. Self-
Test or RF Loopback disconnects the Demodulator from the IF receive input connector.
4.2 DMD2401 LB/ST Fault Philosophy
The DMD2401LB/ST performs a high degree of self-monitoring and fault isolation. The alarms are
separated into three categories; Active Alarms, Common Equipment Alarms, and Latched Alarms. Also,
a feature exists that allows the user to ‘Mask’ out certain Alarms as explained below.
4.2.1 Alarm Masks
The user has the capability to ‘Mask’ individual alarms on the DMD2401. When an Alarm is masked, the
front panel LEDs and the Fault Relays do not get asserted, but the Alarm will still be displayed. This
feature is very helpful during debugging or to lock out a failure that the user is already aware of.
4.2.2 Active Alarms