Check Receive Vco - Tait TM9100 Service Manual

Check that the correct receive frequency is synthesized. This is the
Task 17 —

Check Receive VCO

frequency of the receive VCO output
Figure
1.
2.
3.
4.
5.
194 Frequency Synthesizer Fault Finding
9.9.
Enter the CCTM command 335 0 to set the transmit-receive switch
off (receive mode).
Using a frequency counter, proceed as follows to observe the receive
frequency at the port before and after grounding the junction
RX
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:
RX port: maximum receive 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 receive frequency measured in
If it is incorrect, go to Task
Task 20.
Proceed as follows to observe the receive 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:
RX port: minimum receive 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 receive frequency measured in
If it is incorrect, go to Task
Task 20.
1 at the
SYN RX LO RX
Figure 9.9):
RX
Table 9.2)
Table
Step 2 is correct, go to
19, but if no frequency is detected, go to
Figure
port, use the tweezers to
RX
Table 9.2)
Step 4 is correct, go to
19. If no frequency is detected, go to
TM9100 Service Manual
© Tait Electronics Limited August 2005
port shown in
port, use a pair
9.2.
Step 4.
port
RX
9.9):
Table 9.2.
Task 18.