Comtech EF Data SDM-650B - Manual (Page 156)

Maintenance SDM-650B Satellite Modem
6–12 Rev. 6
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. 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.
AGC-LEVL Output power level fault.
Typically indicates that the level at the modulator output is not the level that
is programmed. Replace the modulator card and return it for repair.
MODULE Modulator module fault.
Typically 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 M&C
card, or in the interface between the modulator and M&C card. Return the
defective card for repair.
6.2.2 Demodulator/Decoder Faults (Dmd_Flts Menu)
Fault Possible Problem and Action
C_DETECT Typically 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 that the demodulator has an RF input at the proper frequency
and power level. Check that the demodulator data rate is properly
programmed. Refer to the fault isolation procedure for TCLK_SYN in
Section 6.2.1. Verify the frequency of the data transmitted from the
modulator is within 100 PPM. Look at the test points on the demodulator
and decoder for the eye pattern, data, and clock per Sections 6.1.3.2 and
6.1.3.3 to verify proper levels, activity, and phase.
RF_SYN Demodulator synthesizer is faulted.
Return the demodulator for repair.
DATA_CLK Typically indicates a loss of lock on the reference of the demodulator clock
recovery oscillator.
Return the decoder card for repair.