Part 1 Of 3; Figure 5-22. Rx Back-End-Poor Sinad Or No Audio (380-470 Mhz And 450-520 Mhz) - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

5-32
5.6.18 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?
Yes
Measure Second LO
at C5058, top side
towards Abacus III
(U5002) pin
Signal
present?
Yes
Frequency is
107.4 or 111.9
MHz?
Yes
Measure Abacus
0-3V Digital SSI
lines FS,DOUTA,
and CLKOUT
Are the
levels 0-3V?
Yes
Frequency
CLKOUT at
1.2MHz?
Yes
FS = 20kHz
sync pulse?
Yes
Figure 5-22. RX Back-End—Poor SINAD or No Audio (380–470 MHz and 450–520 MHz)—Part 1 of 3
May 25, 2005
Refer back to
No
Receiver IF
troubleshooting
flowchart
Voltage
No
level of >~4.3V
at Q5002
Collector?
Voltage
No
level of ~1.7V
1
at Q5002 Base
(pin 1)?
Visually inspect
the Second
LO VCO
Visual
No
examination
3
OK?
No problem
found
No
2
No
3
Troubleshooting Charts: Flowcharts
Check Voltage Regulator
U0505 for normal operation,
No
look for base to emitter
drop of ~0.7V on Q5001,
replace if necessary
Yes
Inspect biasing components
No
and solder. Replace Q5002
as necessary
Yes
No
Make repairs
as necessary
Yes
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
No
3
6881096C74-B