6815854H01-A June 15, 2005
Troubleshooting Charts: Flowcharts 5-29
5.6.18 RX Back-End—Poor SINAD or No Audio (380–470 MHz and 450–520 MHz)—
Part 1 of 3
Figure 5-20. RX Back-End—Poor SINAD or No Audio (380–470 MHz and 450–520 MHz)—Part 1 of 3
Is the
IF level at
R5034 ~+20dB
relative to the
RF input?
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Signal
present?
Voltage
level of >~4.3V
at Q5002
Collector?
Voltage
level of ~1.7V
at Q5002 Base
(pin 1)?
Measure Second LO
at C5058, top side
towards Abacus III
(U5002) pin
Refer back to
Receiver IF
troubleshooting
flowchart
Measure Abacus
0-3V Digital SSI
lines FS,DOUTA,
and CLKOUT
3
2
3
1
Are the
levels 0-3V?
No
Yes
Yes
Frequency
CLKOUT at
1.2MHz?
No
3
No
FS = 20kHz
sync pulse?
Frequency is
107.4 or 111.9
MHz?
Inspect biasing components
and solder. Replace Q5002
as necessary
Yes
Visually inspect
the Second
LO VCO
Yes
No
Visual
examination
OK?
Make repairs
as necessary
No problem
found
DOUTA=
24 bit I, 24
bit Q, 8 bit AGC word
(similar to fig X-X,
troubleshooting
waveforms)?
Yes
Go on to RX audio
troubleshooting
flowchart
Check Voltage Regulator
U0505 for normal operation,
look for base to emitter
drop of ~0.7V on Q5001,
replace if necessary
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