186 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 31 —
Check Transmit-
Receive Switch
If no frequency is detected in the check of the VCO, first check that the
transmit-receive switch is functioning correctly.
1. Resolder R542 in position (see Figure 11.12).
2. Remove the
VCO BOT can.
3. Enter the CCTM command 335 0 to switch on the supply to the
RX
port.
4. Measure the voltage at pin 2 of D5004 (see Figure 11.13). (Some
RF noise might be observed.) The voltage should be:
5. Enter the CCTM command 335 1 to switch off the supply.
6. Again measure the voltage at pin 2 of D5004.
7. If the voltages measured in Step 4 and Step 6 are correct, go to
Step 8. If they are not, the switching network is suspect; go to
Task 32
.
8. Enter the CCTM command 335 1 to switch on the supply to the
TX
port.
9. Measure the voltage at pin 1 of D5004 (see Figure 11.13). (Some
RF noise might be observed.) The voltage should be:
10. Enter the CCTM command 335 0 to switch off the supply.
11. Again measure the voltage at pin 1 of D5004.
12. If the voltages measured in Step 9 and Step 11 are correct, go to
Task 33
. If they are not, the switching network is suspect; go to
Task 32
.
pin 2 of D5004: 5.0 ± 0.3 V DC (after entry of CCTM 335 0)
pin 2 of D5004: 0 V DC (after entry of CCTM 335 1)
pin 1 of D5004: 5.0 ± 0.3 V DC (after entry of CCTM 335 1)
pin 1 of D5004: 2.1 ± 0.4 V DC (after entry of CCTM 335 0)
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