Tait TM8100 mobiles, Service Manual

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206 Frequency Synthesizer Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 14 —
Check Feedback
Voltage
If the loop filter is suspect but the reference voltage is correct, check the
feedback voltage.
1. Measure the feedback voltage at pin 6 of IC505 (see Figure 9.4 ).
The result should be:
2. If the voltage is not correct, the loop filter is faulty; go to Step 3 .
If the voltage is correct, resolder R542 in position (see Figure 9.8 )
and go to Task 15 .
3. Check IC504 , IC505 , Q511 (see Figure 9.4 ) and associated
components.
4. Check the following components (see Figure 9.8 ):
Note
On early issue boards, C548 is fitted instead of these components.
5. If a fault is found, repair the circuit, repeat the measurement of the
feedback voltage in
Step 1 , and resolder R542 in position
(see Figure 9.8 ).
6. If the feedback voltage is now correct, go to “Final Tasks” on
page 163 . If it is not, or if no fault could be found, replace the board
and go to “Final Tasks” on page 163 .
IC505 pin 6: 2.8
±
0.1V DC
A4 band: C5085 to C5089
B1 band: C5085 to C5089
C0 band: C5085 to C5088
D1 band: C5085 to C5088
H5 band: C5085 and C5086
H6/H7 bands: C5085 and C5086
K5 band: C590 and C591