Rx Back-End-Poor Sinad Or No Audio (700-800 Mhz)-Part 1 Of 3 - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

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5.6.36 RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 1 of 3
START
Poor SINAD or
No Audio
Is the
IF level at
TP6350~+20dB
relative to the
RF input?
Measure Second LO
at C6026, top side
towards Abacus III
(U6000) pin
Signal
present?
Frequency
is 75.6 or 71.1
MHz?
Measure Abacus
0-3V Digital SSI
lines FS,DOUTA,
and CLKOUT
Are the
levels 0-3V?
Frequency
CLKOUT at
1.2MHz?
FS = 20kHz
sync pulse?
Figure 5-38. RX Back-End—Poor SINAD or No Audio (700–800 MHz)—Part 1 of 3
May 25, 2005
No
Yes
No
Yes
No
1
Yes
No
3
Yes
No
2
Yes
No
3
Yes
Troubleshooting Charts: Flowcharts
Refer back to
Receiver IF
troubleshooting
flowchart
Check Voltage Regulator
Voltage
U0505 for normal operation,
No
level of >~3.5V
look for base to emitter
at Q6000
drop of ~1.2V on Q6001,
Collector?
Yes
Voltage
Inspect biasing components
No
level of ~2.15V
and solder. Replace Q6000
at Q6000 Base
(pin 1)?
Yes
Visually inspect
the Second
LO VCO
Visual
No
Make repairs
examination
as necessary
OK?
Yes
No problem
found
DOUTA=
24-bit I, 24-bit Q,
8-bit AGC word?
Yes
Go on to RX audio
troubleshooting
flowchart
replace if necessary
as necessary
No
3
MAEPF-27806-O
6881096C74-B