Check Transmit Vco - Tait TM9100 Service Manual

Check that the correct transmit frequency is synthesized. This is the
Task 23 —

Check Transmit VCO

frequency of the transmit VCO output
Figure
1.
2.
3.
4.
5.
202 Frequency Synthesizer Fault Finding
9.9.
Enter the CCTM command 335 1 to set the transmit-receive switch
on (transmit mode).
Using a frequency counter, proceed as follows to observe the transmit
frequency at the port before and after grounding the junction
TX
between C541 and R547 (see
While holding the probe from the counter on the
of tweezers to momentarily ground the junction. The frequency
should change to:
TX port: maximum transmit frequency (see
The loop filter will hold its output steady at 13.3 V. This should result
in a frequency equal to the maximum given in
If the transmit frequency measured in
If it is incorrect, go to Task
Task 26.
Proceed as follows to observe the transmit frequency at the
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
momentarily 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:
TX port: minimum transmit frequency (see
The loop filter will hold its output steady at about 0V. This should
result in a frequency equal to the minimum given in
If the transmit frequency measured in
If it is incorrect, go to Task
Task 26.
at the port shown in
SYN TX LO TX
Figure 9.9):
TX
Table 9.3)
Table
Step 2 is correct, go to
25. If no frequency is detected, go to
Figure 9.9):
port, use the tweezers to
TX
Table 9.3)
Step 4 is correct, go to
25. If no frequency is detected, go to
TM9100 Service Manual
© Tait Electronics Limited August 2005
port, use a pair
9.3.
Step 4.
port
TX
Table 9.3.
Task 24.