Rx Back-End-Poor Sinad Or No Audio (136-174 Mhz)-Part 1 Of 3 - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

5-18
5.6.4 RX Back-End—Poor SINAD or No Audio (136–174 MHz)—Part 1 of 3
Is the
IF level at
______~+16dB
relative to the
RF input?
Yes
easure Second LO
at C3207, top side
towards Abacus III
(U3000) pin
Signal
present?
Yes
Frequency
is 107.4
Hz?
Yes
easure Abacus
0-3V Digital SSI
lines FS,DOUTA,
and CLKOUT
Are the
levels 0-3V?
Yes
Frequency
CLKOUT at
1.2 Hz?
Yes
FS = 20kHz
sync pulse?
Yes
Figure 5-8. RX Back-End—Poor SINAD or No Audio (136–174 MHz)—Part 1 of 3
May 25, 2005
Refer back to
No
Receiver IF
troubleshooting
flowchart
Voltage
No
level of >~3.5V
at Q3000
Collector?
Voltage
No
level of ~3.5V
1
at Q3000 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
Q3001 for normal operation,
No
look for base to emitter
drop of ~1.2V on Q3001,
replace if necessary
Yes
Inspect biasing components
No
and solder. Replace Q3000
as necessary
Yes
No
ake repairs
as necessary
Yes
DOUTA=
24 bit I, 24
bit Q, 8 bit AGC word
(similar to fig X-X,
troubleshooting
waveforms)?
Yes
ake repairs
as necessary
No
3
AEPF-27806-O_VHF
6881096C74-B