Motorola ASTRO Digital Saber Service Manual page 98

No TX Modulation
(Vocoder Failure)
Verify standard bias
per Table 3.
Isolate and
Standard
repair problems.
bias OK?
See chart C.5.
Set radio to test mode CSQ.
Connect radio to R4005B test box
or equivalent and inject a 1KHz
mic signal with amplitude
sufficient to provide 3KHz
deviation (about 11mV RMS).
PTT radio using external
PTT switch. Verify signals
top of radio is
per Figs. W8 and W10.
Verify signals per Figs. W8
and W10.
Fault lies with
transceiver board.
Fig. W8-
Yes All signals No
Refer to appropriate
Trace 1
present?
chart. "No Transmit
present?
Deviation" V/U - C.28
800MHz - C.27
Replace
Speaker/Mic/Flex
Fig. W8-
Yes
assembly after
Trace 3
verifying continuity
present?
of signal paths.
Synopsis
This failure indicates a lack of
transmit modulation with the
fault lying with the vocoder. It
assumes no power up fail codes
were displayed. Since all
modulation modes occur
through the same path, this Replace U406 if
failure applies to digital/ continuity of
PL,DPL, etc. Failure modes are
signals
as follows:
EXT/INT_SPKR
1) Error with host µC in which
and MICEN from
PTT is not detected. U401 to U406
2) Missing DSP IRQB interrupt. verifies and PTT
3) Missing clock or data on SSI was initiated
port from/to ADSIC.
from external.
4) Non functional control of or
*Note: Q401 ia a
faulty Audio PA.
non-inverting
5) Damaged microphone or flex.
transistor buffer.
6) Faulty ADSIC IC.
Replace U401.
Trace PTT (int/ext)
from switch to
No
Verify LED on
U206 and correct
opens. If no
lit RED.
problems found,
replace U206.
Yes
No Check and repair
Replace U406.
Q402 inverter
circuit as
necessary.
If signal is present
Yes
during this test, but
not under normal
conditions (internal
Maybe
mic.) check MUX
circuitry of U408
and U412 and
microphone bias
elements
R434/R406 and
Yes
R430/R408.
1
1
Verify signals at U401 are:
Fig. W8-
No
Signal Logic
Trace 4
EXT/INT_SPKR 0
present?
MICEN 1
Yes
Control
No
signals
Fig. W8-Trace 2
correct?
present?
Yes
No
Verify 1KHz
signal at U401-
EXTMICIN.
Verify signals per
Fig. W3 at indicated
points.
Yes
Audio signal
present at
input to
U401?
Fig. W3-
No
Traces 1 and
3 present?
Verify MUX control
voltages:
Signal Logic
U408-4 0 Yes
U412-4 1
Fig. W3-Trace 2
present?
No
MUX control
voltages
check?
Yes
Yes
Replace U406.
Verify operation
of MUXs U408 and
U412.
MAEPF-24418-A
No
Replace as
MUXs verify?
necessary.
Yes
Repair limiter
circuit comprised
of U411 and
associated
circuitry.
10-16
Fault lies with
transceiver board.
Yes
Refer to appropriate
chart. "No Transmit
Deviation" V/U - C.28
800MHz - C.27
No
Replace U406.
No
Replace U405.
Chart 26 . No TX Modulation