Service manual

Troubleshooting Charts 5-15
68P81076C25-C July 1, 2002
Chart C.20 No TX Modulation
No Tx Modulation
Signal
present?
Check for continuity
between U406
and U401.
Signal
present?
Signal
present?
Signals
present?
Check for continuity
between U401
and U523.
PTT radio using
microphone.
Verify 1KHz signal
present at output
of U523.
MAEPF-26076-O
Replace U406.
Replace U405.
Replace U406.
Replace U530.
Replace U402.
Replace part.
Verify that Q541 and
Q554 are good.
Verify 1KHz signal
present at U401.
Verify 1KHz signal
present at U523.
Verify
control lines.
Troubleshoot
RF board.
Verify 1KHz signal
present at J500-1.
Repair connection
or replace Q542.
Verify data
goes into U530.
Verify that data is
getting to U530.
Troubleshoot VOCON
board data lines.
Verify signals per
Waveform W3 at
indicated points.
Verify audio at
input to U524
pin 4.
Verify pin 1 of
U530 goes Hi
on PTT.
Verify 1KHz signal
present at input
of U402.
No
Replace U406.
No
Yes
Yes
Signal
present?
No
Signal
present?
No
Signals
present?
Yes
Signal
present?
Yes
No
No
No
No
Yes
No
1
Yes
Verify control
signals at U524.
Ext Mic Hi
VRX TX audio Low
No
Control
signals
correct?
Standard
bias OK?
No
Yes
No
1
2
No
Fig. W8
Trace 4
present?
Yes
No
No
Functional?
Replace U524.
Yes
Yes
Signal
present?
Yes
Signals
present?
No
Yes
Fig. W3
Trace 1 and 3
present?
Yes
Repair connection.
Replace U401.
Replace U523.
Replace U402.
Repair connection.
Replace U530.
Repair connection.
No
Continuity?
Yes
Yes
Yes
No
No
Fig. W3
Trace 2
present?
Yes
Fig. W8
Trace 2
present?
Yes
Verify standard
bias per Table 6.
Isolate and
repair problems,
See Chart C.5.
Verify TX LED is
on in display of
control head.
Verify signal per
Figs. W8
and W10.
Signal
present?
Yes
Yes
1
˚ 2
Fig. W8
Trace 1
present?
No
LED on?
No
Yes
Fig. W8
Trace 3
present?
No
Yes
Inject a 80 mV
1KHz mic. signal
into the microphone
connector.
Trace PTT line from
PTT switch to U522
and on to U206.
Correct problems.
Trace Mic Hi line back
to the microphone
connector and
correct problem.
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.