TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 223
© Tait Electronics Limited November 2007
6. If the voltages are correct, go to Step 7. If they are not, check the
transmit buffer circuitry based on IC506 (see Figure 9.11). If this
repairs the fault, conclude with Step 14.
7. Remove the
VCO BOT can.
8. Check the VCO buffer amplifier in receive mode. Enter the CCTM
command 335 1 to set the transmit-receive switch off.
9. Measure the voltage at the base of Q510 (see Figure 9.12).
10. Check the VCO buffer amplifier in transmit mode. Enter the CCTM
command 335 1 to set the transmit-receive switch on.
11. Measure the voltage at the base of Q510.
12. If the voltages are correct, the transmit VCO is suspect. Go to
Step 13. If they are not, check the VCO buffer circuitry based on
Q510 (see Figure 9.12). If this repairs the fault, conclude with
Step 14.
13. Check the transmit VCO circuitry based on Q509
(see Figure 9.11). Conclude with Step 14.
14. 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 163. If they are
not, or if no fault could be found, replace the board and go to “Final
Tasks” on page 163.
base of Q510: 0V DC (receive mode)
base of Q510: 0.7 ± 0.1V DC (transmit mode)
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