No Tx Modulation - Motorola ASTRO Digital Spectra Service Manual

Troubleshooting Charts

No Tx Modulation

Verify standard
bias per Table 6.
Isolate and
No
Standard
repair problems,
bias OK?
See Chart C.5.
Yes
Inject a 80 mV
1KHz mic. signal
into the microphone
connector.
PTT radio using
microphone.
Verify TX LED is
on in display of
control head.
Trace PTT line from
No
PTT switch to U522
LED on?
and on to U206.
Correct problems.
Yes
Verify signal per
Figs. W8
and W10.
Fig. W8
Yes No
Signal
Trace 1
1
present?
present?
Trace Mic Hi line back
Fig. W8
No
to the microphone
Trace 3
connector and
present?
correct problem.
˚ 2
68P81076C25-C
Synopsis
This failure indicates a lack of
transmit modulation with the
fault lying with the VOCON or
Command board. It assumes no
power up 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 C in which
PTT is not detected.
2) Missing DSP IRQB interrupt.
3) Missing clock or data on SSI
port from/to ADSIC.
4) Damaged microphone.
5) Faulty ADSIC IC.
Yes
Verify 1KHz signal
present at J500-1.
Yes Signal
Troubleshoot
present?
RF board.
No
Verify 1KHz signal
No
present at input
Replace U406.
of U402.
Yes
No
Signal
Repair connection.
present?
Yes
Yes
Replace U402.
1
Verify 1KHz signal
present at U401.
Check for continuity
No
Signal
between U406
present?
and U401.
Yes
Verify 1KHz signal
present at U523.
Check for continuity
Signal No
between U401
present?
and U523.
Yes
No
Verify 1KHz signal Continuity?
Repair connection.
present at output
of U523.
Yes
Replace U401.
Signal
present?
No
Repair connection
Verify
control lines. or replace Q542.
No
Verify pin 1 of
Signals No
Signal
U530 goes Hi
present? present?
on PTT.
Yes Yes
Replace U523. Verify data
goes into U530.
No
Signals
Repair connection.
present?
Verify control
signals at U524.
Ext Mic Hi
VRX TX audio Low
Control
Verify audio at
Yes
signals
input to U524
correct?
pin 4.
No
No
Signal
Replace U524.
present? Verify that Q541 and
Q554 are good.
Yes
Replace U402.
No
Functional?
Replace part.
Yes
Verify that data is
getting to U530.
No
Troubleshoot VOCON Signals
present?
board data lines.
Yes
Replace U530.
Yes
Replace U530.
5-15
2
Fig. W8
No
Trace 4
present?
Yes
Fig. W8
Yes
1
Trace 2
present?
No
Verify signals per
Waveform W3 at
indicated points.
Fig. W3
No
Trace 1 and 3 Replace U406.
present?
Yes
Fig. W3
No
Replace U405.
Trace 2
present?
Yes
Replace U406.
MAEPF-26076-O
Chart C.20 No TX Modulation
July 1, 2002