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 Ta s k 1 5
.
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
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