TM8100/TM8200 Service Manual Frequency Synthesizer Fault Finding 213
© Tait Electronics Limited November 2007
Task 18 —
Repair PLL feedback
If both the minimum and maximum receive frequencies are correct, the
PLL feedback is suspect.
1. Resolder R542 in position (see Figure 9.11).
2. Remove the
VCO BOT can.
3. Replace the components C567, R574 (see Figure 9.12) and IC503
(see Figure 9.11).
4. Also check the second stage of the receive buffer amplifier based on
IC5100 (see Figure 9.12). Repair any fault.
5. Confirm that the fault in the radio has been removed. If it has, go to
“Final Tasks” on page 163. If it has not, replace the board and go to
“Final Tasks” on page 163.
Task 19 —
Repair Receive VCO
If either or both the minimum and maximum receive frequencies are
incorrect, the receive VCO circuitry is faulty.
1. For all bands except K5, remove the
VCO TOP can.
For the K5 band, remove the
VCO BOT can.
2. Check the receive VCO. The circuitry is based on Q504
(see Figure 9.11 for all bands except K5 and Figure 9.12 for the
K5 band).
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 1 7
.
5. If the frequencies are now correct, resolder R542 in position
(see Figure 9.11), and go to “Final Tasks” on page 163. If they are
still not correct, go to Step 6.
6. Resolder R542 in position (see Figure 9.11). Replace the board and
go to “Final Tasks” on page 163.
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