Tait TM8100 mobiles, Service Manual

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TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 231
© Tait Electronics Limited November 2007
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 9.14 ).
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 9.15 ). (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 9.15 ). (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
±
0.3V DC (after entry of CCTM 335 0)
pin 2 of D5004: 0V DC (after entry of CCTM 335 1)
pin 1 of D5004: 5.0
±
0.3V DC (after entry of CCTM 335 1)
pin 1 of D5004: 2.1
±
0.4V DC (after entry of CCTM 335 0)