Tait TB7100, Service Manual

Page: 170 / 370

172 Frequency Synthesizer Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
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 11.9 ).
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 11.9 ). 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
±
0.3 V DC (after entry of CCTM 335 0)
pin 3 of Q506: 0 V DC (after entry of CCTM 335 1)