Tx Or Rx Vco Unlock (Fail 001) (136-174 Mhz)-Part 1 Of 2 - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

Troubleshooting Charts: Flowcharts
5.6.9 TX or RX VCO Unlock (Fail 001) (136–174 MHz)—Part 1 of 2
TX or RX VCO
Unlock (Fail 001)
"Sniff" Frequency
near TX or RX
VCO shield or
injection string
Frequency
Detected?
Yes
Check VCO
Control Voltage
at TP6756
<.6VDC or
>11.5VDC or
drifting?
Yes
12VDC
at Charge Pump
Capacitor
C3822?
Yes
Go to Transmitter
or receiver
Injection string
troubleshooting
charts
Figure 5-13. TX or RX VCO Unlock (Fail 001) (136–174 MHz)—Part 1 of 2
6881096C74-B
Place an Inductive field probe
connected to a spectrum analyzer
near area to be sniffed.
8.2VDC
No
No
at Q3756-C
Collector?
Yes
3.0VDC
on pins 5, 36,
and 13 of
U3751?
No
Check Voltage
No
ultiplier
Circuitry
Check 9.3 Volt
supply path from
regulator U0950 in
Controller section
No
Check if VCO
is locked using
spectrum analyzer
No
Locked?
Yes
3VDC
No
at pin 4 of
U3751?
Yes
Go to
Controller
troubleshooting
charts
5-23
A
Go to Transmitter
or receiver
Injection string
troubleshooting
charts
Check for short
on pin 4 to
controller or
replace U3751
AEPF-27812-O_VHF
May 25, 2005