Tait TP9100 - Page 189

TP9100 Service Manual Frequency Synthesizer Fault Finding 189
© Tait Electronics Limited May 2005
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 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 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 R720 (see Figure 9.7) and go to
Step 4.
4. Enter the CCTM command 335 0 and measure the voltage at the via
between R720 (see Figure 9.7) and the digital circuitry.
5. Enter the CCTM command 335 1 and again measure the voltage at
the via between R720 and the digital circuitry.
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; resolder R720 in
position (see Figure 9.7), replace the main board and go to “Final
Tasks” on page 134.
7. Check and resolder R720 in position (see Figure 9.7), and check for
continuity between Q508 and the digital circuitry via R593
(see Figure 9.11) 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 4
V3 DEC switches
(based on Q506, Q507 and Q508) (see Figure 9.3).
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.
R593: 0V DC (after entry of CCTM 335 0)
R593: 2.0 ± 0.5V DC (after entry of CCTM 335 1)
via at R720: 0V DC (after entry of CCTM 335 0)
via at R720: 3.3 ± 0.3V DC (after entry of CCTM 335 1)