Tait TM8100 mobiles Service Manual page 211

Task 17 —
Check Receive VCO
TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Check that the correct receive frequency is synthesized. This is the
frequency of the receive VCO output
Figure 9.11.
Enter the CCTM command 335 0 to set the transmit-receive switch
1.
off (receive mode).
2. Using a frequency counter, proceed as follows to observe the receive
frequency at the
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 13.3V (14.7V for the K5
band). This should result in a frequency equal to the maximum given
in Table 9.3.
3. If the receive frequency measured in
If it is incorrect, go to
Task 20.
4. Proceed as follows to observe the receive frequency at the
before and after applying 3V DC to the junction of C541 and R547;
there is a convenient 3V level at R544 (see
While holding the probe on the
momentarily apply 3V 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
5. If the receive frequency measured in
If it is incorrect, go to
Task 20.
SYN RX LO
port before and after grounding the junction
RX
Figure
Table
Step 2
Task 19, but if no frequency is detected, go to
port, use the tweezers to
RX
Table
Step 4
Task 19. If no frequency is detected, go to
Frequency Synthesizer Fault Finding
1 at the
port shown in
RX
9.11):
port, use a pair
RX
9.3)
is correct, go to Step
RX
Figure 9.11):
9.3)
Table 9.3.
is correct, go to Task
4.
port
18.
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