Technical Manual

10-26
Chart 24. Bootstrap Fail
Replace U406 if
continuity of
signals
EXT/INT_SPKR
and MICEN from
U718 to U406
verifies and PTT
was initiated
from external.
*Note: Q401 ia a
non-inverting
transistor buffer.
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
failure applies to digital/
PL,DPL, etc. Failure modes are
as follows:
1) Error with host µC in which
PTT is not detected.
2) Missing DSP IRQB interrupt.
3) Missing clock or data on SSI
port from/to ADSIC.
4) Non functional control of or
faulty Audio PA.
7) Damaged 50-pin or 20-pin
compression connector.
5) Damaged microphone or flex.
6) Faulty ADSIC IC.
Isolate and
repair problems.
See chart C.5.
No TX Modulation
(Vocoder Failure)
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).
Standard
bias OK?
Verify standard bias
per Table 3.
Yes
Verify signals per Figs. W8
and W10.
All signals
present?
Replace
front cover (housing)
verifying continuity
of signal paths.
1
1
No
Fig. W8-
Trace 1
present?
Replace U406.
No
Fig. W8-
Trace 3
present?
Yes
Yes
Yes
Fig. W8-
Trace 4
present?
Yes
No
Verify signals at U718 are:
Signal Logic
EXT/INT_SPKR 0
MICEN 1
Control
signals
correct?
Verify 1KHz
signal at U718-18
EXTMICIN.
Yes
No
Replace U718.
Audio signal
present at
input to
U718?
Yes
No
Verify MUX control
voltages:
Signal Logic
U712-4 0
U713-4 1
MUX control
voltages
check?
Check and repair
Q107 inverter
circuit as
necessary.
No
Yes
MAEPF-26038-O
Verify operation
of MUXs U712 and
U713.
MUXs verify?
Replace as
necessary.
No
Yes
Repair limiter
circuit comprised
of U714 and
associated
circuitry.
If signal is present
during this test, but
not under normal
conditions (internal
mic.) check MUX
circuitry of U712
and U713 and
microphone bias
elements
R193/R194 and
R197/R198.
Maybe
Fig. W8-Trace 2
present?
Yes
Fault lies with
transceiver board.
Refer to appropriate
chart. "No Transmit
Deviation" V/U - C.28
800MHz - C.27
No
Verify signals per
Fig. W3 at indicated
points.
Fig. W3-Trace 2
present?
No
Fig. W3-
Traces 1 and
3 present?
Replace U406.
Replace U405.
No
Yes
Yes
PTT radio using external
PTT switch. Verify signals
per Figs. W8 and W10.
Verify LED on
top of radio is
lit RED.
Trace PTT (int/ext)
from switch to
U702 and correct
opens. If no
problems found,
replace U702.
Yes
No
Replace U406.
Fault lies with
transceiver board.
Refer to appropriate
chart. "No Transmit
Deviation" V/U - C.28
800MHz - C.27