Tait TP9100 - Page 204

204 Frequency Synthesizer Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 33 —
Check Buffer
Amplifier
If no VCO frequency is detected but the switching network is not faulty,
check the buffer amplifier. If the amplifier is not faulty, there might be a fault
in the VCO that was not detected earlier.
1. Enter the CCTM command 335 0 to set the transmit-receive switch
to receive.
2. Measure the voltage at pin A1 of D510 (see Figure 9.17). (Some RF
noise might be observed.)
3. Measure the voltage at the collector of Q5000 (see Figure 9.17).
4. If the voltages measured in Step 2 and Step 3 are not correct, go to
Step 5. If they are, check the VCO circuitry based on Q504
(see Figure 9.17). Conclude with Step 6.
5. The buffer amplifier is suspect. Check the buffer circuitry (based on
Q5000, IC506) (see Figure 9.17).
6. 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 134. If they are
not, or if no fault could be found, replace the main board and go to
“Final Tasks” on page 134.
pin A1 of D510: 1.6V DC
collector of Q5000: 0.7 ± 0.2V DC