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ategory 2 Failures - No Error Message, but Nonfunctional
Measurement
his group includes the A3 fractional-N/reference, A4 source board assemblies, and A5 receiver
board assemblies. ypical problems include:
Phase lock lost
ransmission trace not close to 0 dB
Power output problems
Other RF problems
Troubleshooting the A3 Fractional-N/ eference Assembly
Check the Output Power
Connect a power meter or spectrum analyzer to the RF OU port. Set the analyzer to a CW
frequency of 300 kHz in trigger-hold mode. Change power level and see if output power
changes correctly. Repeat at several di erent frequencies (i.e. 1 MHz and 50 MHz).
If there is little or no source output, or a transmission trace is exceptionally noisy:
he source may be disconnected from the receiver. Check the cable connections between
the source and receiver (torque to 10 inch-lbs). If the problem persists, go to \Phase Lock
Problems" below.
If little or no output power is available on an HP 8713C/14C:
It is possible that the analyzer was subjected to excessive reverse power or a high level of
ESD. In either case, the built-in source limiter may have opened (somewhat like a fuse). his
source limiter is located on the A5 receiver and can be replaced separately as an individual
component. If RF power is available at the output of the A4 source board but not at the output
of the A5 receiver, then suspect the limiter. his can easily be checked with a continuity
checker between the two center pins.
If the signal is not steady (i.e. appears unlocked), or if the frequency doesn't change
properly):
Go to \Phase Lock Problems." If the signal appears okay but the power levels are incorrect, go
to \Power Problems." Otherwise, proceed to the \ roubleshooting Receiver Problems."
Phase Lock Problems
here are three phase lock loops on the source board: RF1, RF2, and the source LO. As you
can see from the overall block diagram at the end of this chapter, the source LO is mixed with
the RF1 signal to produce the source RF output. It is also mixed with the RF2 signal to produce
the receiver LO output.
Since both the RF1 and RF2 loops use the 10 MHz reference signal from the
A3 fractional-N/reference board, rst verify the accuracy of that signal.
To verify the 10 MHz reference signal:
Remove the handles and front panel. Connect an oscilloscope and/or frequency counter
to A3J3 (the connector on the right) to measure the 10 MHz output from the A3
fractional-N/reference board.
T roubleshoot ng and Block D agrams
4-17
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