Tait TM8100 mobiles, Service Manual

Page: 220 / 620

220 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
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 9.11 ).
2. Remove the
VCO BOT
can.
3. Replace the components C570 , R578 (see Figure 9.12 ) and IC503
(see Figure 9.11 ).
4. 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 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 for all
bands except K5 and Q509 for the K5 band (see Figure 9.11 ).
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 9.11 ), 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 .