Comtech EF Data SDM-300A - Manual (Page 351)

SDM-300A Satellite Modem Revision 6
Troubleshooting MN/SDM300A.IOM
18–15
18.3.3.3 Transmit Interface Faults
Fault/Alarm Possible Problem and Action
TX DROP Drop interface hardware fault (D&I only).
The typical cause of this fault is the drop phase-locked loop is not locked, or some other drop interface
hardware has malfunctioned. Contact the Comtech EF Data Customer Support Department.
TX DATA/AIS Data or incoming AIS.
When the AIS is selected in the Interface Utility menu for TX data fault, the transmit interface fault TX
data/AIS is monitoring a fault condition of all 1s from customer data input to the modem. When data is
selected in the Interface Utility menu for TX data fault, the TX interface fault TX data/AIS is monitoring
a fault condition of all 1s or 0s. This is referred to as a data-stable condition (data is not transitioning).
This fault indicates there is trouble in the chain sending data to the modem. The modem passes this
signal transparently, and takes no other action. This indication is a monitor function only, and aids in
isolating the trouble source in a system.
TX CLOCK PLL Transmitter phase-locked loop fault.
Indicates the transmitter PLL is not locked to the reference of the interface transmit clock recovery
oscillator. Contact the Comtech EF Data Customer Support Department.
TX CLOCK ACT Activity detector alarm of the selected interface transmit clock.
Indicates the selected TX clock is not being detected. Check the signal of the selected TX clock
source to verify the signal is present. The interface will fall back to the internal clock when this alarm is
active.