Comtech EF Data SDM-309B - Manual (Page 158)

SDM-309B Satellite Modem Maintenance
MN/U-SDM309B Rev. # 6-6–13
6.2 Fault Isolation
System faults are reported in the “FAULT” menu (Figure 3-3). Stored faults are reported
in the ‘sTFAULTS” menu (Figures 3-4 through 3-6). The following list is to be used in
isolating the problem and deciding the appropriate action to be taken.
6.2.1 Modulator Faults
Refer to Sections 3.1.6.1, 3.2.5.1, and Figures 3-3 and 3-4 of the O&I manual.
Fault Possible Problem And Action
RF_SYN Modulator synthesizer is faulted.
This is considered a major alarm and will turn off the modulator output.
Return the modulator module for repair.
DATA_CLK Incoming data clock activity fault.
This fault is not considered a major alarm and will not turn off the modulator
output. Problem is most likely on the interface card or external to the
modem.
Check to see that the incoming data clock is present at the modem DATA
I/O connector. If data and clock are present at the DATA I/O, then replace
the interface card to clear the fault and return for repair.
TCLK_SYN This fault is an indication that the internal clock VCO has not locked to the
incoming data clock or the internal clock synthesizer has not locked to the
internal reference. This is considered a major alarm and will turn off the
modulator output. Check to see that the proper data rate has been set up
and selected. Verify the incoming data rate to match what has been
selected in the modem. Refer to Table 6.2 for available data rates for the
SDM 309. Or refer to Intelsat document IESS 309 for available data rates
for the SDM 309 modem In the SDM 309 the internal reference is changed
to account for the IBS overhead of 16/15. An SDM 309 would be
programmed for the input data rate to the channel unit. The modem
accounts for the overhead because of the change in internal reference.
Verify the frequency of the input data clock to be within the lock range of
100PPM.
If the inputs to the modem are all correct then the problem could be in one
of two locations. Check the modulator first by replacing it with a spare. If the
problem still exists replace the interface card. When the fault has been
isolated to a single card send that card back for repair.
I_CHANNL Activity alarm for the I channel digital filter.
This alarm is considered a major alarm and will turn off the modulator
output.
An alarm in this position indicates either a fault in the scrambler or if the
scrambler is disabled it indicates a loss of incoming data. If the fault is
active with the scrambler turned OFF check to see that there is input data
at the DATA I/O connector. If data is present replace the interface card to
clear the fault and return the interface card for repair. If the fault is active
with the scrambler turned ON replace the modulator card and return it for
repair.
Q_CHANNL Activity alarm for the Q channel digital filter.
Follow the same procedure as for the I channel.
AGC_LEVL Output power level fault. Indicates that the level at the modulator output is
not the level that is programmed. Replace the modulator card and return it
for repair.