Vhf Receiver Front-End Hybrid - Motorola ASTRO Digital Spectra Plus Service Manual

5-18
START
Check Module Gain: Inject
Measure Transceiver 160MHz -20dBm at J9127
Sinad by Injecting
Measure at IF Output
Signal at J9127
Is
Sinad
No Problem with
Yes
<-120 with Preamp
Preamp; >-22 Non-
RX Front End or
<-117 non-
RF Board
Preamp
?
No
Measure Sinad
Inject 106.5 MHz
into RF Board
at J350
Sinad Measure RF Level
Troubleshoot
No
<- 120
at Input of 1st
RF Board
?
Mixer
Yes
Check DC
Voltage at IF Preamp; >-17 dBm
Non-Preamp
Output Pad
Is
Troubleshoot
Check Inject Level
Voltage
No
DC Feed from
~ _
at Injection Input Pad
9.6V
RF Board
?
Yes
Check Biasing
on Q3202:
Vcollector ~ _ 7.5V
~ _ 0.9 to 1.6V
Vbase
Is
Check Bias Circuit Check 1st Mixer and
Voltage At No
and Associated Associated Components
Q3202 OK
Components Replace as Necessary
?
Yes
Chart C.24 VHF Receiver Front-End Hybrid
October 28, 2002
Is
Recheck RF Board and
>-13 with Yes
Transceiver Sinad
Preamp
?
No
Is
>-7dBm with
No Check the Preselector
and its Components
Replace as Necessary
?
Yes
Is
Troubleshoot
Level No
RF Injection or
> _
+ 20dBm
Carrier Board
?
Yes
Troubleshooting Charts
6881076C25-D