Tait TP9100 Service Manual

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TP9100 Service Manual Frequency Synthesizer Fault Finding 203© Tait Electronics Limited May 2005Task 32 óRepair SwitchingNetworkIf the transmit-receive switch is not functioning correctly, first check the DIGSYN TR SW line to confirm that the digital circuitry is not the cause. If thedigital circuitry is not faulty, the switching network is suspect.1. Enter the CCTM command 335 0 to set the transmit-receive switchoff (receive mode). Measure the voltage at the end of theDIG SYN TR SW line at R576 (see Figure 9.17).2. Enter the CCTM command 335 1 to set the transmit-receive switchon (transmit mode). Again measure the voltage at R576.3. If the voltages measured in Step 1 and Step 2 are correct, go toStep 9. If they are not, go to Step 4.4. Enter the CCTM command 335 0 and measure the voltage at the leftside of R720 (see Figure 9.7).5. Enter the CCTM command 335 1 and again measure the voltage atthe left side of R720.6. If the voltages measured in Step 4 and Step 5 are correct, go toStep 7. If they are not, the digital circuitry is faulty; replace the mainboard 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” onpage 134. If the repair failed, replace the main board and go to “FinalTasks” on page 134.9. Check the circuitry for the transmit-receive and 3V switches (basedon Q515 and Q510) (see Figure 9.17).10. If a fault is found, repair the circuit, confirm that the voltages are nowcorrect, and go to “Final Tasks” on page 134. If the repair failed orthe fault could not be found, replace the main board and go to “FinalTasks” 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)