214 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
Task 24 —
Repair PLL feedback
If both the minimum and maximum transmit frequencies are correct, the
PLL feedback is suspect.
1. Resolder R542 in position (see Figure 9.10).
2. Remove the
VCO BOT can.
3. Replace the components C570, R578 (see Figure 9.11) and IC503
(see Figure 9.10).
4. Confirm that the fault in the radio has been removed. If it has, go to
“Final Tasks” on page 157. If it has not, replace the board and go to
“Final Tasks” on page 157.
Task 25 —
Repair Transmit
VCO
If either or both the minimum and maximum transmit frequencies are
incorrect, the transmit VCO circuitry is faulty.
1. Remove the
VCO TOP can.
2. Check the transmit VCO. The circuitry is based on Q510
(see Figure 9.10).
3. If a fault is found, repair it and go to Step 4. If no fault is found, go
to Step 6.
4. Repeat the frequency measurements in Step 2 and Step 4 of Tas k 23
.
5. If the frequencies are now correct, resolder R542 in position
(see Figure 9.10), and go to “Final Tasks” on page 157. If they are
still not correct, go to Step 6.
6. Resolder R542 in position (see Figure 9.10). Replace the board and
go to “Final Tasks” on page 157.
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