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Front End Control Troubleshooting
A15 Front End Control Assembly Troubleshooting
Monitor the purple wires on each connector, one at a time. The purple wire
starts at ~21.5 VDC. When switching from uW Preselector Bypass to Standard
Path, you should see a negative going pulse to 0 VDC on the oscilloscope for
~15 mS before the voltage returns to ~21.5 VDC steady state.
If both the green wires and the purple wires measure this pulse correctly, the
control logic from the A15, Front End Controller board is operating correctly.
The black wire is ground.
RF Signal Tracing
Refer to Chapter 4, “RF Section Troubleshooting” for this method of
troubleshooting if you are unable to use an oscilloscope
Verifying Narrowband IF Out (A15J900)
The outer cover and top shield need to be removed to verify A15J900 I.F.
output to the A2 Analog IF assembly. Refer to Chapter 14, “Assembly
Replacement Procedures” for the removal procedure. Press Mode, Spectrum
Analyzer, Mode Preset on the analyzer. Press Input/Output, RF Calibrator, 50
MHz, Freq, 50 MHz, Span, 0 Hz, Amptd, Attenuation, 10 dB, Amptd, More 1
of 2, Internal Preamp Off, System, Alignments, Auto Align, Off. Disconnect
the cable marked J900 that plugs into the top of the A15, Front End Controller
board and connect a functioning spectrum analyzer where the cable was
plugged in. J900's output should be 322.5 MHz at ~-28 dBm on the
functioning spectrum analyzer if the Front End Controller board is switching
this level correctly. If -28 dBm is not being measured correctly, remove the
cable labeled J902 from the Front End Controller board and measure the
output of that cable. This should also measure 322.5 MHz at ~-28 dBm. If the
output of the J902 cable measures correctly and yet the output of J900 is
incorrect, the most probable cause is the A15, Front End Controller board.
Reconnect all cables to their correct location when finished with the
measurements.
IMPORTANT When plugging in an mmcx connector, a distinct “snap” should be heard
when the cable is seated correctly.
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