Tait TM8100 mobiles Service Manual page 206

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