Tait TP9100 - Page 202

202 Frequency Synthesizer Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 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 9.15).
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 the junction of L525 and C594
(see Figure 9.17). (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 the junction of L525 and C594.
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
Ta sk 3 2
.
8. Enter the CCTM command 335 1 to switch on the supply to the
TX
port.
9. Measure the voltage at the junction of L5001 and C596
(see Figure 9.17). (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 the junction of L5001 and C596.
12. If the voltages measured in Step 9 and Step 11 are correct, go to
Ta sk 3 3
. If they are not, the switching network is suspect; go to
Ta sk 3 2
.
junction of L525/C594: 3.0 ± 0.1V DC (after entry of CCTM 335 0)
junction of L525/C594: 0V DC (after entry of CCTM 335 1)
junction of L5001/C596: 3.0 ± 0.1V DC (after entry of CCTM 335 1)
junction of L5001/C596: 2.1 ± 0.4V DC (after entry of CCTM 335 0)