Tx Or Rx Vco Unlock (Fail 001) (700-800 Mhz)-Part 1 Of 2 - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

5-56
5.6.42 TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 1 of 2
TX or RX VCO
Unlock (Fail 001)
"Sniff" Frequency
near TX or RX
VCO shield or
infection string
Frequency
Detected?
Yes
Check VCO
Control Voltage
at TP6759
<.6VDC or
>11.5VDC or
drifting?
Yes
12VDC
at Charge Pump
Capacitor
C6768?
Yes
Go to Transmitter
or receiver
Injection string
troubleshooting
charts
Figure 5-44. TX or RX VCO Unlock (Fail 001) (700–800 MHz)—Part 1 of 2
May 25, 2005
Place an Inductive field probe
connected to a spectrum analyzer
near area to be sniffed.
8.2VDC
No
at Q6759
Collector?
Yes
3.0VDC
on pins 5, 36,
and 13 of
U6751?
Yes
Check Controller
Section and/or
ABACUS IC
U6000
No
Check Voltage
No
Multiplier
Circuitry
Check 9.3 Volt
No
supply path from
regulator U0950 in
Controller section
No
Check if VCO
is locked using
spectrum analyzer
Locked?
Yes
3VDC
at pin 4 of
U6751?
Yes
Go to
Controller
troubleshooting
charts
Troubleshooting Charts: Flowcharts
A
Go to Transmitter
or receiver
No
Injection string
troubleshooting
charts
Check for short
No
on pin 4 to
controller or
replace U6751
MAEPF-27812-O
6881096C74-B