Service manual

5-18 Troubleshooting Charts
July 1, 2002 68P81076C25-C
Chart C.24 VHF Receiver Front-End Hybrid
START
Measure
Transceiver
Sinad by Injecting
at J9127Signal
Sinad
<-120 with Preamp
?
Yes
No
No
No
No
Yes
Yes
No
Yes
Yes
Yes
No
No
Yes
No Problem with
RX Front End or
RF Board
Measure Sinad
Inject 106.5 MHz
into RF Board
at J350
Sinad
<- 120
?
Troubleshoot
RF Board
Check DC
Voltage at IF
Output Pad
9.6V
?
Troubleshoot
DC Feed from
RF Board
~
_
Check Biasing
on Q3202:
Vcollector
~
_
7.5V
Vbase
?
Check Bias Circuit
and Associated
Components
Check Module Gain: Inject
Measure RF Level
at Input of 1st
Check Inject Level
at Injection Input Pad
Troubleshoot
RF Injection or
Carrier Board
+ 20dBm
?
>
_
160MHz -20dBm at J9127
Measure at IF Output
Is
<-117 non-
Preamp
Is
Voltage
~
_
0.9 to 1.6V
Is
Voltage At
Q3202 OK
Is
>-13 with
Preamp; >-22 Non-
Preamp
?
Recheck RF
Board and
Transceiver
Sinad
Mixer
Is
>-7dBm with
Preamp; >-17 dBm
Non-Preamp
?
Check the Preselector
and its Components
Replace as Necessary
Is
Level
Check 1st Mixer and
Associated Components
Replace as Necessary