116 Chapter 5
Troubleshooting the Synthesizer Section
Verifying the A12 Synthesizer Board
Dual Loop troubleshooting
If an LO unlock problem occurs only in dual loop mode (span < 2 MHz)
the cause is either the A12A2 Sampling Oscillator board or the sampler
circuit on the A12A1. The A12A2 board is only used in dual loop mode.
To verify the problem is the A12A2 you must measure the sampling
oscillator output at A12A2 J1. The following table lists PSA center
frequency verses sample oscillator frequency at J1. J1 is a female
MMCX connector. Use the MMCX to SMB cable supplied in the service
kit. The three frequencies test the low, middle and high frequency range
of the sample oscillator. If the frequencies are correct, yet the unlock
appears, suspect the A12A1 synthesizer board. If the frequencies are
incorrect or there is no output signal, suspect A12A2.
PSA settings: Span 100 kHz
Measuring Spectrum Analyzer: Span 20 kHz
Single loop troubleshooting
When single loop mode (span ≥ 2 MHz) is bad, it will appear that dual
loop is also bad, suspect the A12A1 board.
E4440-60049 Extender Board
The E4440-60049 extender board is used to troubleshoot the A10 3rd
Converter, A11 Reference, A12 Synthesizer, and A13 Front End Driver
assemblies.
Refer to Figure 5-1. There are eight SMB connectors and eight switches
on the E4440-60049 extender board. Each switch controls the signal
path at the corresponding connector to allow for signal monitoring and
injection. For example, switch S6 controls the signal path for connector
P6. The following table shows how the switches work:
PSA Center
Frequency (MHz)
Sampling Oscillator
Output (MHz)
Power Level
636 642.187 +12 dBm
228 700.781 +12 dBm
508 747.656 +12 dBm
Extender Board Switch Positions
Up - “Board to SMB” Connects SMB connectors to J2.
Middle - “Board to Mother” Connects J1 to J2.
Up - “SMB to Mother” Connects J1 to SMB connectors.
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