Tait TP9100, Service Manual, Page: 159 / 326

TP9100 Service Manual
Frequency Synthesizer Fault Finding 159
© Tait Electronics Limited May 2005
9 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 9.1 . 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 9.1 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