216
Frequency Synthesizer Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
November 2007
Task 21 —
Repair Switching
Network
If the transmit-receive switch is not functioning correctly, first check the
DIG
SYN
TR
SW
line to confirm that the digital board is not the cause. If the digital
board is not faulty, the switching network is suspect.
1.
Enter the CCTM command
335 0
to set the transmit-receive switch
off (receive mode). Measure the voltage on the
DIG SYN TR SW
line
between
Q508
and
R593
(see
Figure 9.11
).
2.
Enter the CCTM command
335 1
to set the transmit-receive switch
on (transmit mode). Again measure the voltage at
R593
.
3.
If the voltages measured in
Step 1
and
Step 2
are correct, go to
Step 9
. If they are not, remove
R103
(see
Figure 9.7
) and go to
Step 4
.
4.
Enter the CCTM command
335 0
and measure the voltage at the via
between
R103
and the digital board (see
Figure 9.7
).
5.
Enter the CCTM command
335 1
and again measure the voltage at
the via between
R103
and the digital board.
6.
If the voltages measured in
Step 4
and
Step 5
are correct, go to
Step 7
. If they are not, the digital board is faulty; resolder
R103
in
position (see
Figure 9.7
), replace the board and go to
“Final Tasks”
on page 163
.
7.
Check and resolder
R103
in position (see
Figure 9.7
), and check for
continuity between
Q508
and the digital board via
R593
(see
Figure 9.11
) and R103.
8.
If no fault is found, go to
Step 9
. If a fault is found, repair the circuit,
confirm that the voltages are now correct, and go to
“Final Tasks” on
page 163
If the repair failed, replace the board and go to
“Final
Tasks” on page 163
.
9.
Check the circuitry for the transmit-receive and 5V switches (based
on
Q506
,
Q507
and
Q508
) (see
Figure 9.11
).
10.
If a fault is found, repair the circuit, confirm that the voltages are now
correct, and go to
“Final Tasks” on page 163
. If the repair failed or
the fault could not be found, replace the board and go to
“Final
Tasks” on page 163
.
R593: 0V DC (after entry of CCTM 335 0)
R593: 2.0
±
0.5V DC (after entry of CCTM 335 1)
via at R103: 0V DC (after entry of CCTM 335 0)
via at R103: 3.3
±
0.3V DC (after entry of CCTM 335 1)
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