10-28
Chart 27. No RX Audio
Synopsis
This failure indicates a lack of
received audio with the fault
lying with the vocoder. It
assumes a functional
transceiver board and no power
up fail codes were displayed.
Since all received signal modes
occur through this same path,
this failure applies to digital/
PL,DPL, etc. Failure modes are
as follows:
1) Missing DSP IRQB interrupt.
2) Lack of 2.4 REF clock and/or
data from ABACUS.
3) Missing clock or data on SSI
port from ADSIC.
4) Non functional control of or
faulty Audio PA.
5) Damaged speaker or speaker
flex.
7) Damaged 50-pin or 20-pin
compression connectors.
6) Faulty ADSIC.
Isolate and
repair problems.
See chart C.5.
No Receive Audio
(Vocoder Failure)
Set radio to test mode
CSQ. Inject a 1KHz
modulated signal at the
carrier frequency at
-60dBm level with
3KHz deviation.
Standard
bias OK?
Verify standard bias
per Table 3.
Yes
No
Verify signals
present at ADSIC
(U406) per Fig. W10
and Fig. W5. Note
DOUT and DOUT* are
low level voltage
signals.
Signals
present?
During a mode
change, verify an
ABACUS
programming
sequence occurs
per Fig. W4
probing on the
ABACUS carrier.
ABACUS is
programmed?
Verify SBI,
connections
between ADSIC and
ABACUS ICs.
Repair as
necessary. If
connection good,
replace U406.
No
Yes
Fault lies with
transceiver board.
Refer to appropriate
section. Chart C.30
Verify signals per
Fig. W7 at points
indicated.
Signals
present?
Replace
front cover (housing)
assembly after
verifying continuity
of signal paths.
Fig. W7-
Trace 1
present?
1
Yes
No
1
Replace U406.
Fig. W7-
Trace 2
present?
No
Yes
Verify signals per Fig.
W2 at points
indicated.
Signals
present?
No
No
Replace U406.
Yes
Yes
Fig. W7-
Trace 3 or 4
not present or
in phase?
Verify signals
EXT/INT_SPKR
and AMPEN at
U718 are logic
high.
Replace
front cover (housing)
assembly after
verifying continuity
of signal paths.
No
Yes
Control
signals
correct?
Replace U718.
Yes
MAEPF-26041-O
No
Replace U406 if continuity
of signals EXT/INT_SPKR
and AMPEN from U718 to
U406 verifies..
At this point the fault
could lie with a faulty
ADSIC, or it could be
the DSP does not
see/service the IRQB
or SC1 interrupt from
ADSIC!
Check for continuity
between U405 and
U406 of the signals
depicted in Fig. W2
and the 8KHz IRQB.
Connections
good?
Repair
connections.
No
Yes
Perform radio
function which
causes an alert
tone to be
generated.
Alert tone
audible?
Replace U405.
Replace U406.
No
Yes
Make sure no
external
mic/speaker is
attached to
universal
connector which
would cause the
radios to select
EXT_SPKR.
No
Yes
D out, D out*, ODC
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