Motorola APX 3000 Detailed Service Manual page 128

5-38
5.12 VCO Failure – Page 1(VHF, UHF1, UHF2, 7/800MHz)
Check parts around U702. If OK,
replace U702.
No
Check if VCO is lock at desired
frequency using field probe.
No
VCO locked?
Yes
Check lock_det line
circuitry in controller section.
Check R2811 and R2812
for continuity
VCO Failure
Note: "Sniff": Using an inductive field probe as
"Sniff" frequency near
VCO shield (SH15)
No
Frequency Detected?
Yes
Remove FGU
shield (SH6)
Check control voltage
at R705
< 0.3Vdc or
> 10.6Vdc or
voltage drifting?
Yes
Check power on
prescaler buffer output.
C823 using field probe.
Is power at
No
C823 >
- 15dBm?
Yes
Check loop filter R701,
No
R705, C703, C707,
C713 for continuity fault.
Yes
Replace suspected components.
Troubleshooting Charts: VCO Failure
an antenna to measure frequency. Place
the probe approximately 1/2 inch away
from component to be sniffed.
Remove VCO shield
(SH15)
UHF1
radio?
No
7/800 MHz
radio?
No
UHF2
radio?
No
VHF
radio?
No
No fault found
Yes
1
Yes
2
Yes
3
Yes
4