208
Frequency Synthesizer Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
November 2007
Task 16 —
Check
TP
503 Test
Point
If the reference voltage, feedback voltage, and
DIG
SYN
FAST
line are all
correct, check the voltage at the
TP
503
test point.
1.
Measure the voltage at the
TP
503
test point
(see
Figure 9.8
).
The oscilloscope should show a DC level less than 3.0V with no sign
of noise or modulation.
2.
If the correct result is obtained, go to
Step 3
. If it is not, go to
Step 5
.
3.
The loop filter is faulty but the above measurements do not provide
more specific information. Check
IC504
,
IC505
,
Q511
(see
Figure 9.4
) and associated components.
4.
Check the following components (see
Figure 9.8
), then conclude
with
Step 9
:
Note
On early issue boards,
C548
may be fitted instead of these
components.
5.
Remove
R566
and
R570
(see
Figure 9.8
), which provide a
modulation path to the VCO(s).
6.
Repeat the measurement of
Step 1
.
7.
If the correct result is now obtained, go to
Step 8
. If the correct result
is still not obtained, the CODEC and audio circuitry is suspect;
resolder
R566
and
R570
in position (see
Figure 9.8
), and go to
“CODEC and Audio Fault Finding” on page 399
.
8.
Resolder
R566
and
R570
in position (see
Figure 9.8
).
9.
Check
IC504
(pins 6, 8, 9) (see
Figure 9.4
) and the associated
components in the loop filter.
10.
If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to
“Final Tasks” on page 163
. If they are
not, or if no fault could be found, replace the board and go to
“Final
Tasks” on page 163
.
TP503 test point: < 3.0V DC
A4 band:
C5085
to
C5089
B1 band:
C5085
to
C5089
C0 band:
C5085
to
C5088
D1 band:
C5085
to
C5088
G2 band:
C5085
and
C5086
H5 band:
C5085
and
C5086
H6/H7 bands:
C5085
and
C5086
K5 band:
C590
and
C591
Содержание TM8100 mobiles
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