Tait TB7100, Service Manual

Page: 353 / 370

TB7100 Service Manual CODEC and Audio Fault Finding 355
© Tait Electronics Limited October 2005
Task 8 —
Check Signal
from CODEC
First generate an appropriate audio test signal and check whether the signal
is present at the output of the CODEC circuitry.
1. Enter the CCTM command
400 x
, where
x
is a valid channel number.
(A suitable channel will depend on the programming of the radio.)
2. Enter the CCTM command 21 to force unmuting of the received
audio signal.
3. Enter the CCTM command
110 128
to set the audio level at its
midpoint.
4. At the test set apply 60%, 1 kHz modulation to the RF signal. Reduce
the volume to a minimum.
5. Enter the CCTM command
324 r5
.
6. Check that the received signal is present at pin 2 (
AUD TAP OUT
) of the
internal-options connector SK102 (see Figure 15.5 ) (alternatively,
the measurement point for
CDC AUD TAP OUT
shown in Figure 15.4 ).
The signal should be:
7. If the above signal is correct, go to Step 8 . If it is not, go to Task 9 .
8. Check the components in the path from pin 13 of the auxiliary
connector SK101 to the CODEC and audio circuitry. These are
C719
and L708 (see Figure 15.6 ) and the link R747
(see Figure 15.5 ). Also check the auxiliary connector itself. Repair
any fault.
9. Confirm the removal of the fault and go to Step 10 . If the repair failed
or the fault could not be found, replace the main-board assembly and
go to
“Final Tasks” on page 123 .
10. If there is also a fault with the transmit modulation, notwithstanding
modulation at the auxiliary connector, go to
Task 15 of “Faulty
Modulation Using Auxiliary Connector” on page 366 . If there is no
other fault, go to “Final Tasks” on page 123 .
pin 2 of internal-options connector: received signal with 2.4V DC offset