Tait TM8100 mobiles, Service Manual

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TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 215
© Tait Electronics Limited November 2007
Task 20 —
Check Switching
to Receive Mode
If no receive frequency is detected in the check of the receive VCO, first
check that the transmit-receive switch is functioning correctly.
1. Resolder R542 in position (see Figure 9.11 ).
2. Enter the CCTM command
335 0
to switch on the supply to the
receive VCO.
3. Measure the voltage at the first collector (pin 3) of Q506
(see Figure 9.11 ). The voltage should be:
4. Enter the CCTM command 335 1 to switch off the supply.
5. Again measure the voltage at the first collector of Q506 .
6. If the voltages measured in Step 3 and Step 5 are correct, go to
Task 22 . If they are not, the switching network is suspect; go to
Task 21 .
pin 3 of Q506: 5.0
±
0.3V DC (after entry of CCTM 335 0)
pin 3 of Q506: 0V DC (after entry of CCTM 335 1)