200
Frequency Synthesizer Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
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
).
The result should be:
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
.
3.
Check
IC504
,
IC505
,
Q511
(see
) and associated
components.
4.
Check the following components (see
):
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
, and resolder
R542
in position
(see
).
6.
If the feedback voltage is now correct, go to
. If it is not, or if no fault could be found, replace the board
and go to
.
IC505 pin 6:
2.8
±
0.1 V 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 band:
C5085
and
C5086
Содержание TM8235
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