
192
Frequency Synthesizer Fault Finding
TP9100 Service Manual
© Tait Electronics Limited
May 2005
Task 23 —
Check Transmit VCO
Check that the correct transmit frequency is synthesized. This is the
frequency of the transmit VCO output
SYN
TX
LO
at the
TX
port shown in
1.
Enter the CCTM command
335 1
to set the transmit-receive switch
on (transmit mode).
2.
Using a frequency counter, proceed as follows to observe the transmit
frequency at the
TX
port before and after grounding the junction
between
C541
and
R547
(see
While holding the probe from the counter on the
TX
port, use a pair
of tweezers to momentarily ground the junction. The frequency
should change to:
The loop filter will hold its output steady at 13.3 V. This should result
in a frequency equal to the maximum given in
.
3.
If the transmit frequency measured in
is correct, go to
.
If it is incorrect, go to
. If no frequency is detected, go to
.
4.
Proceed as follows to observe the transmit frequency at the
TX
port
before and after applying 3 V DC to the junction of
C541
and
R547
;
there is a convenient 3 V level at
R544
(see
):
While holding the probe on the
TX
port, use the tweezers to momen-
tarily apply 3 V DC to the junction; do not touch the board with your
hand, and do not allow the tweezers to touch any cans when you
remove them. The frequency should change to:
The loop filter will hold its output steady at about 0V. This should
result in a frequency equal to the minimum given in
.
5.
If the transmit frequency measured in
If it is incorrect, go to
. If no frequency is detected, go to
.
TX port: maximum transmit frequency (see
)
TX port: minimum transmit frequency (see
Содержание TP9100
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