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Maintenance
MODULE
6.2.2 Demodulator Faults
Refer to Sections 3.1.6.2, 3.2.5.2, and Figures 3-3 and 3-5 in the O&I manual.
C_DETECT
RF_SYN
DATA_CLK
I_CHANNL
Q_CHANNL
BERTHRSH
MODULE
6-6–14
Modulator module fault. Indicates a problem in programming the modulator
card. Check to see that the modulator card is present and is properly
seated. If the modulator card is properly seated this could indicate a
problem in the Monitor and Control (M&C) card or in the interface between
the modulator and M&C card. Return the defective card for repair.
Fault
Indicates loss of decoder lock.
This is the most common fault displayed in the modem. Any problem from
the input data on the modulator end of the circuit to the output of the
decoder can cause this alarm.
Check first of all to see that the demodulator has an RF input at the proper
frequency and power level.
Check to see that the demodulator data rate is properly programmed.
Refer to the fault isolation procedure for TCLK_SYN in the modulator
Section 6.2.1. Verify the frequency of the data transmitted from the
modulator is within 100PPM. Look at the test points on the demodulator
and decoder for the eye pattern, data, and clock per Section 6.1. to verify
proper levels, activity, and phase.
Demodulator synthesizer is faulted. Return the demodulator for repair.
Indicates a loss of lock on the reference of the demodulator clock recovery
oscillator. Return the decoder card for repair.
Indicates a loss of activity in the I channel of the quadrature demodulator.
Typically indicates a problem in the modulator side of the circuit.
Check for proper RF input to the demodulator. If the input to the
demodulator is correct then the problem is in the baseband filter on the
daughter card on the demodulator, in the soft decision circuitry on the
demodulator, or it is in the decoder costas processor.
Replace either the demodulator card or the decoder card to isolate the
fault and return the failed card for repair.
Indicates a loss of activity in the Q channel of the quadrature demodulator.
Follow the same procedure as with the I channel fault.
Indication that the preset BER threshold has been exceeded.
Setting of this alarm is done in the "UTILITY" menu. This is an alarm based
on the corrected BER reading on the front panel.
Demodulator module fault. Indicates a problem in programming the
demodulator card.
Check to see that the demodulator card and the decoder card are present
and are properly seated. If the cards are properly seated this could indicate
a problem in the Monitor and Control (M&C) card or in the interface
between the decoder card and M&C card. Return the defective card for
repair.
SDM-309B Satellite Modem
Possible Problem And Action
MN/U-SDM309B Rev. #
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