Service manual

Troubleshooting Charts 5-17
68P81076C25-C July 1, 2002
Chart C.22 800 MHz Receiver Front-End Hybrid Chart C.23 UHF Receiver Front-End Hybrid
START
Measure
Transceiver
Sinad by Injecting
at J9127Signal
Yes
No
Sinad
<- 119
?
Yes
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No Problem with
RX Front End or
RF Board
Measure RF Board
Sinad: Inject
109.65MHz into RF
Board at J350
Sinad
<- 119
?
Troubleshoot
RF Board
Check DC
Voltage at IF
Output Pad
9.6V
?
Troubleshoot
DC Feed from
RF Board
~
_
~
_
Check Biasing
on Q8126:
Vcollector
~
_
8.0V
Vbase = 0.4 to 0.8V
OK
?
Check Bias Circuit
and Associated
Components
Check Module Gain: Inject
On-Channel Signal
(851-870 MHz) of -20dBm
at J9127: Measure Level 109.65
MHz Out at IF Output Pad
Check Beta
of Q8126
Replace Q8126
Measure RF Level
at Base of Q8126
Recheck RF BD
and Transceiver
Sinad
Measure Level of
On-Channel Signal
at Preselector
Input Pad
Check Inject Level
at Injection Input Pad
Troubleshoot
RF Injection or
Carrier Board
Replace
RXFE Board
Check Components
in Output Network
C8129, 30, 31, 36:
L8129, 30, 31:
R8129, 30, 31:
Replace as
Necessary
-10 dBm
to -14 dBm
?
B = <60
?
-1 dBm
?
+ 3 dBm
?
>
_
-20 to -23 dBm
?
START
Measure
Transceiver
Sinad by Injecting
at J9127Signal
Yes
No
Sinad
<- 120
?
Yes
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No Problem with
RX Front End or
RF Board
Measure RF Board
Sinad: Inject
109.65MHz into RF
Board at J350
Sinad
<- 120
?
Troubleshoot
RF Board
Check DC
Voltage at IF
Output Pad
12V
?
Troubleshoot
DC Feed from
RF Board
~
_
~
_
Check Biasing
on Q9125:
Vcollector
~
_
10V
Vbase = 0.4 to 0.8V
OK
?
Check Bias Circuit
and Associated
Components
Check Module Gain: Inject
Check Beta
of Q9125
Replace Q9125
Measure RF Level
at Base of Q9125
Recheck RF BD
and Transceiver
Sinad
Measure Level
at Preselector
Input Pad
Check Injection Level
at Injection Input Pad
Troubleshoot
RF Injection or
Carrier Board
Replace
RXFE Board
Check Components
in Output Network
Replace as
Necessary
-20 dBm
to -17 dBm
?
B = >60
?
-10 dBm
?
+ 10dBm
?
>
_
-20 dBm
?
Signal -20dBm at J9127
Measure at IF Output Pad
~~
~