Comtech EF Data SDM-650B - Manual (Page 160)

Maintenance SDM-650B Satellite Modem
6–16 Rev. 6
6.3.2 Receive Faults (RX_INTF)
The faults listed below are only displayed when the ASYNC overhead channel unit is
installed.
Fault Possible Problem and Action
BUF_UNFL Buffer Underflow. The plesiochronous buffer has underflowed.
As buffer underflow is normally a momentary fault (there are clock problems if
this is continuously present). This is included in this section to be consistent
with the fault reporting system and be correctly registered in the stored fault
memory. The time and date of the last 10 receive OFU faults are stored in
battery-backed memory as an aid to troubleshooting. The interval between
stored overflow/underflow events can be used to determine the accuracy of
the relative clock.
BUF_OVFL Buffer Overflow. The plesiochronous buffer has overflowed.
As buffer overflow is normally a momentary fault, there will be clock problems
if this is continuously present. This is included in this section to be consistent
with the fault reporting system and be correctly registered in the stored fault
memory. The time and date of the last 10 receive OFU faults are stored in
battery-backed memory as an aid to troubleshooting. The interval between
stored overflow/underflow events can be used to determine the accuracy of
the relative clock.
RX_PLL Indicates a loss of lock on the reference of the interface receive clock
recovery oscillator.
Return the interface card for repair.
BUFF_CLK Loss of activity on the selected buffer clock source.
The modem will fallback to the satellite clock.
MUX_Lock Demultiplexer Synchronization Lock Fault. This fault means that the
demultiplexer is unable to maintain valid frame and multiframe alignment.
The usual cause is invalid or absent receive data. This is a major (prompt)
alarm. It will cause insertion of receive Alarm Indication Signal (all 1s) and
switchover will be attempted. This fault is to be sent as a backward alarm to
the distant end. This fault will occur when no carrier is present, but will
probably never occur with a correct signal.