394
CODEC and Audio Fault Finding
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
Task 9 —
Check LPF and
Buffer Amplifier
If there is no test signal at the internal-options connector, then either
CODEC 1 is faulty or there is a fault in the LPF or buffer amplifier.
1.
Remove the
CDC
BOT
can.
2.
Check the signal at the junction between
R224
and
IC204
(see
). This should be:
3.
If the above signal is correct, go to
. If it is not, CODEC 1
(
IC204
) is faulty; replace the board and go to
4.
Check the voltage at pin 1 of
IC201
(see
5.
If the voltage is correct, go to
. If it is not, check the LPF circuit
based on
IC201
(pins 1 to 3) (see
). Repair any fault and
conclude with
6.
Check the voltage at pin 7 of
IC201
(see
7.
If the voltage is correct, go to
. If it is not, check the buffer
amplifier based on
IC201
(pins 5 to 7) (see
fault and conclude with
8.
Check
R207
and
R208
(see
). Repair any fault and
conclude with
9.
Confirm the removal of the fault and go to
. If the repair failed
or the fault could not be found, replace the board and go to
.
10.
If there is also a fault with the transmit modulation, notwithstanding
modulation at the auxiliary connector, go to
Using Auxiliary Connector” on page 402
. If there is no other fault,
junction of R224 and IC204: 0.7V
pp
with 2.4V DC offset
pin 1 of IC201: 1.2V
pin 7 of IC201: 2.4V
Содержание TM8235
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