Tait TB7100, Руководство по обслуживанию

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TB7100 Service Manual Frequency Synthesizer Fault Finding 143
© Tait Electronics Limited October 2005
11 Frequency Synthesizer Fault Finding
Introduction
This section covers the diagnosis of faults in the frequency synthesizer.
The sections are divided into the following:
■
Initial checks
■
Fault diagnosis of RF PLL circuitry
■
Fault diagnosis of FCL circuitry
The initial checks will indicate whether it is the RF PLL or the FCL that is
suspect. Note that the synthesizer is a closed-loop control system. A fault in
one area can cause symptoms to appear elsewhere. Locating the fault can
therefore be difficult.
Measurement
Techniques
The radio must be in CCTM for all the fault-diagnosis procedures of this
section. The CCTM commands required are listed in
Table 11.1 .
Full details of the commands are given in “Computer-Controlled Test
Mode (CCTM)” on page 91 . Use an oscilloscope with a x10 probe for all
voltage measurements required. The signals should appear stable and clean.
Consider any noise or unidentified oscillations as evidence of a fault
requiring investigation. Use a frequency counter for all measurements of
high frequencies. The RF power output from the frequency synthesizer will
not exceed 10 mW. If a probe is used for frequency measurements, use the
x1 setting.
Table 11.1 CCTM commands required for the diagnosis of faults in the frequency synthesizer
Command Description
72
101
x y 0
205
301 0 10
302 0 10
334 x
335 x
389 x
393 1 x
Read lock status of RF PLL, FCL and LO2 — displays xyz (0=not in lock, 1=in lock)
Set transmit frequency ( x in hertz) and receive frequency ( y in hertz) to specified values
Reset calibration parameters to their default values
Calibrate VCXO of FCL
Calibrate VCO(s) of RF PLL
Set synthesizer on ( x =1) or off ( x =0) via DIG SYN EN line
Set transmit-receive switch on ( x =1) or off ( x =0) via DIG SYN TR SW line
Set synthesizer mode to slow ( x =0) or fast ( x =1)
Write data x to FPGA