TM9100 Service Manual Frequency Synthesizer Fault Finding 203
© Tait Electronics Limited August 2005
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 9.9).
2. Remove the
VCO BOT can.
3. Replace the components C570, R578 (see Figure 9.10) and IC503
(see Figure 9.9).
4. Confirm that the fault in the radio has been removed. If it has, go to
“Final Tasks” on page 147. If it has not, replace the main-board
assembly and go to “Final Tasks” on page 147.
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 9.9).
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 Task 23
.
5. If the frequencies are now correct, resolder R542 in position
(see Figure 9.9), and go to “Final Tasks” on page 147. If they are
still not correct, go to Step 6.
6. Resolder R542 in position (see Figure 9.9). Replace the main-
board assembly and go to “Final Tasks” on page 147.
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