216 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
Task 27 —
Check Transmit
Buffer Amplifier
If no transmit frequency is detected but the switching network is not faulty,
check the transmit buffer amplifier. If the amplifier is not faulty, there might
be a fault in the transmit VCO that was not detected earlier.
1. Remove the
VCO BOT can.
2. Check the transmit buffer amplifier in receive mode: Enter the
CCTM command 335 0 to set the transmit-receive switch off.
3. Measure the voltage at pin 6 of Q5001 (see Figure 9.11).
4. Then check the transmit buffer amplifier in transmit mode: Enter the
CCTM command 335 1 to set the transmit-receive switch on.
5. Again measure the voltage at Q5001.
6. If the voltages are correct, the transmit VCO is suspect; go to Step 7.
If they are not, the transmit buffer amplifier is suspect; go to Step 9.
7. Remove the VCO TOP can.
8. Check the transmit VCO circuitry based on Q510
(see Figure 9.10). Conclude with Step 10.
9. Check the buffer circuitry based on Q5001 (see Figure 9.11).
10. If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to “Final Tasks” on page 157. If they are
not, or if no fault could be found, replace the board and go to “Final
Tasks” on page 157.
pin 6 of Q5001: 0 V DC (receive mode)
pin 6 of Q5001: 0.7 ± 0.1 V DC (transmit mode)
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