TB7100 Service Manual Frequency Synthesizer Fault Finding 185
© Tait Electronics Limited October 2005
Task 30 —
Repair VCO
If either or both the maximum and minimum frequencies are incorrect, the
VCO circuitry is faulty.
1. Remove the
VCO BOT can.
2. Check the VCO. The circuitry is based on Q5000
(see Figure 11.13).
3. If a fault is found, repair it and go to Step 4. If no fault is found, go
to Step 7.
4. Repeat Step 1 and Step 2 of Task 28
to measure the maximum VCO
frequency.
5. Repeat Step 4 and Step 5 of Task 28
to measure the minimum VCO
frequency.
6. If the frequencies are now correct, resolder R542 in position
(see Figure 11.12), and go to “Final Tasks” on page 123. If they are
still not correct, go to Step 7.
7. Resolder R542 in position (see Figure 11.12). Replace the main-
board assembly and go to “Final Tasks” on page 123.
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