Tait TP9100 Service Manual

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TP9100 Service Manual Frequency Synthesizer Fault Finding 159© Tait Electronics Limited May 20059 Frequency Synthesizer Fault FindingIntroduction 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 circuitryThe initial checks will indicate whether it is the RF PLL or the FCL that issuspect. Note that the synthesizer is a closed-loop control system. A fault inone area can cause symptoms to appear elsewhere. Locating the fault cantherefore be difficult.MeasurementTechniques The radio must be in CCTM for all the fault-diagnosis procedures of thissection. The CCTM commands required are listed in Table 9.1. Full detailsof the commands are given in “Computer-Controlled Test Mode(CCTM)” on page 91. Use an oscilloscope with a x10 probe for all voltagemeasurements required. The signals should appear stable and clean.Consider any noise or unidentified oscillations as evidence of a faultrequiring investigation. Use a frequency counter for all measurements ofhigh frequencies. The RF power output from the frequency synthesizer willnot exceed 10mW. If a probe is used for frequency measurements, use thex1 setting.Table 9.1 CCTM commands required for the diagnosis of faults in the frequency synthesizerCommand Description72101 x y 0205301 0 10302 0 10334 x335 x389 x393 1 xRead 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 valuesReset calibration parameters to their default valuesCalibrate VCXO of FCLCalibrate VCO(s) of RF PLLSet synthesizer on (x=1) or off (x=0) via DIG SYN EN lineSet transmit-receive switch on (x=1) or off (x=0) via DIG SYN TR SW lineSet synthesizer mode to slow (x=0) or fast (x=1)Write data x to FPGA