Specifications

APEX™ Exciter Incorporating FLO™ Technology
Exciter Troubleshooting Maintenance and Troubleshooting
2604s500.fm
03/08/07 888-2604-001 Page: 5-21
WARNING: Disconnect primary power prior to servicing.
5.8.4 Troubleshooting Down to the Board Level
Isolating a defective circuit board is relatively easy if the faults appear on one or more of
the status screens. This involves interpreting the faults so that they point to a particular
board. Details of the status screens and their faults are covered in Section 3.4 on page 3-8.
Occasionally, the exciter RF output parameters will not meet specifications and the status
screen faults will not point to a particular board. Troubleshooting these types of problems
down to the board level can be more challenging. Such problems can include, but are not
limited to, low or zero RF output power, irregular spectral response, or excessive MER.
These types of problems require on screen and off screen signal tracing, which requires a
knowledge of the signal path through the exciter. A brief signal path review is given in the
next two headings.
5.8.4.1 Digital Tray Transmission Data Path
See Figure 5-2, on page 5-3, the digital tray layout diagram and Figure 4-2, on page 4-4 for
a signal flow block diagram of the APEX exciter. The signal enters the FPGA modulator
board. From the modulator board, it travels through the controller board to the adaptive
precorrector board. From there it goes to the DAC board, the output of which is the 11.1
MHz first IF signal. The first IF signal goes to the input of the up converter board in the
analog tray.
5.8.4.2 Analog Tray Signal Path
See Figure 4-2, on page 4-4 for a signal flow block diagram of the APEX exciter and
Figure 5-1, on page 5-2 for the analog tray layout diagram. The IF signal enters the up
converter board, the output of which goes to the output amplifier. The output of the output
amplifier goes to the transmitter PA(s) and a sample of the output is connected to the input
multiplexer of the down converter board, along with the other three transmitter system
feedback samples. The output of the down converter board is connected to the input of the
ADC board.
5.8.5 Isolating Problem to the Analog or Digital Tray
Three internal loopback functions are available to help isolate problems to the digital or
analog tray. They are the analog and digital loopback features of the adaptive processing
diagnostics screen, used to determine the health of the digital tray, and the exciter loopback
feature of the down converter board diagnostics screen, used to determine the health of the
entire exciter (digital and analog trays).
After determining which tray has a problem, isolating the defective board in that tray will
be discussed.
5.8.5.1 Checking Operation of the Entire Digital Tray
Two methods are available to verify correct operation of the entire digital signal processing
tray. The first method excludes the DAC board, the ADC board, and the analog tray, and
the second method only excludes the analog tray.