Tait TB7100 - Page 185

TB7100 Service Manual Frequency Synthesizer Fault Finding 187
© Tait Electronics Limited October 2005
Task 32 —
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 at
pin 3 of Q5003 (see Figure 11.13).
2. Enter the CCTM command 335 1 to set the transmit-receive switch
on (transmit mode). Again measure the voltage at Q5003.
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 11.6) 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 11.6).
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 11.6), replace the main-board assembly and go
to “Final Tasks” on page 123.
7. Check and resolder R103 in position (see Figure 11.6), and check
for continuity between Q5003 (see Figure 11.13) and the digital
board via 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 123. If the repair failed, replace the main-board assembly and go
to “Final Tasks” on page 123.
9. Check the circuitry for the transmit-receive and 5V switches (based
on Q5002 and Q5003) (see Figure 11.13).
10. If a fault is found, repair the circuit, confirm that the voltages are now
correct, and go to “Final Tasks” on page 123. If the repair failed or
the fault could not be found, replace the main-board assembly and go
to “Final Tasks” on page 123.
pin 3 of Q5003: 5.0 ± 0.3 V DC (after entry of CCTM 335 0)
pin 3 of Q5003: 0 V DC (after entry of CCTM 335 1)
via at R103: 3.3 ± 0.3 V DC (after entry of CCTM 335 0)
via at R103: 0 V DC (after entry of CCTM 335 1)