Tait TP9100 - Page 203

TP9100 Service Manual Frequency Synthesizer Fault Finding 203
© Tait Electronics Limited May 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 circuitry is not the cause. If the
digital circuitry 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 at the end of the
DIG SYN TR SW line at R576 (see Figure 9.17).
2. Enter the CCTM command 335 1 to set the transmit-receive switch
on (transmit mode). Again measure the voltage at R576.
3. If the voltages measured in Step 1 and Step 2 are correct, go to
Step 9. If they are not, go to Step 4.
4. Enter the CCTM command 335 0 and measure the voltage at the left
side of R720 (see Figure 9.7).
5. Enter the CCTM command 335 1 and again measure the voltage at
the left side of R720.
6. If the voltages measured in Step 4 and Step 5 are correct, go to
Step 7. If they are not, the digital circuitry is faulty; replace the main
board and go to “Final Tasks” on page 134.
7. Check for continuity between R576 (see Figure 9.17) and R720.
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 134. If the repair failed, replace the main board and go to “Final
Tasks” on page 134.
9. Check the circuitry for the transmit-receive and 3V switches (based
on Q515 and Q510) (see Figure 9.17).
10. If a fault is found, repair the circuit, confirm that the voltages are now
correct, and go to “Final Tasks” on page 134. If the repair failed or
the fault could not be found, replace the main board and go to “Final
Tasks” on page 134.
R576: 0V DC (after entry of CCTM 335 0)
R576: 3.0V DC (after entry of CCTM 335 1)
left side of R720: 3.3 ± 0.3V DC (after entry of CCTM 335 0)
left side of R720: 0V DC (after entry of CCTM 335 1)