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SDM-650B Satellite Modem
6.2 Fault Isolation
System faults are reported in the Faults menu. Stored faults are reported in the StFaults
menu. Refer to Chapter 4 for more information.
The following sections list the system faults outlined in Chapter 4. Use the following
information to isolate a problem, and help in deciding the appropriate action to be taken.
6.2.1 Modulator Faults (Mod_Flts Menu)
RF_SYN
DATA_CLK
TCLK_SYN
Rev. 6
Fault
Modulator synthesizer is faulted. This is considered a major alarm, and will
turn OFF the modulator output.
Return the modulator module for repair.
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.
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 matches what has been selected in the modem.
Refer to Table 6-2 for available data rates for the modem. Refer to
INTELSAT document IESS-308 for available data rates for the SDM-308B.
Refer to INTELSAT document IESS-309 for data rates for the SDM-309B. In
the modem and SDM-308B, the data rate must reflect any overhead bit that
are added. In the SDM-309B, the internal reference is changed to account
for the IBS overhead of 16/15. Example for the modem: 1544 kbit/s with
16 kbit/s overhead channel would be programmed to operate at 1568 kbit/s
(1544K + 16K + 8K for framing). A standard modem, or a SDM-308B
operating at rev. 2, would be programmed to the input data rate. An SDM-
308B operating at rev. 3 would be programmed to reflect the 96 kbit/s of
overhead. A 1544 kbit/s rev. 3 IDR is programmed to 1640 kbit/s. An SDM-
309B 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 100 PPM. 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.
Possible Problem and Action
Maintenance
6–11
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