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Maintenance DMD15/DMD15L/DMD15/DMD15LL/DMD15/DMD15LIBS/IDR Satellite Modem
6-2 TM051 – Rev. 5.8
Masking alarms can cause undesirable modem performance.
6.2.1 Alarm Masks
The user has the capability to ‘Mask’ individual alarms on the DMD15/DMD15L. 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.
6.2.2 Active Alarms
6.2.2.1 Major Alarms
Major alarms indicate a modem hardware failure. Major alarms may flash briefly during modem
configuration changes and during power-up but should not stay illuminated. Alarms are grouped
into Transmit alarms and Receive alarms - Transmit and Receive are completely independent.
6.2.2.2 Minor Alarms
Minor alarms indicate that a problem may persist outside the modem such as loss of Terrestrial
Clock, loss of terrestrial data activity, or a detected transmit or receive AIS condition.
Alarms are grouped into Transmit Alarms and Receive Alarms - Transmit and Receive are
completely independent.
6.2.2.3 Latched Alarms
Latched alarms are used to catch intermittent failures. If a fault occurs, the fault indication will be
latched even if the alarm goes away. After the modem is configured and running, it is
recommended that the latched alarms be cleared as a final step.
6.3 DMD15/DMD15L Fault Tree Matrices
Tables 6-1 through 6-3 represent, in matrix form, the faults that may occur within the
DMD15/DMD15L. There are three matrices: Interface/Common Equipment Faults, Tx Faults and
Rx Faults.