Vco Tx/Rx Unlock - Motorola ASTRO XTS 5000 Detailed Service Manual

Troubleshooting Charts: VCO TX/RX Unlock

6.16 VCO TX/RX Unlock

VCO TX/RX
unlock
"Sniff"
frequency near
VCO shield
No
Frequency
detected?
Yes
Check control
voltage at
TP243
<0.6Vdc
No
>11.0Vdc or
drifting?
Yes
Check parts
No
around U202. If
OK, replace U202
68P81094C31-O
Sniff: Using an inductive field probe
as an antenna to measure
frequency. Place the probe
approximately 1/2 inch away
from components to be sniffed.
No
5V at TP3?
Yes
Check parts
No
around U2. If
OK, replace U2
Check if VCO
is locked using
spectrum analyzer
VCO locked?
Yes
Check
VOCON board
Bi-polar Transistor (BJT)
Check parts
around U1. If
OK, replace U2
3V at TP5?
Yes
Remove
VCO shield
Aux.
Yes
line 1 (2,4)
drain voltage
is high?
No
emitter voltage
Check parts
Q301 VC01
around BJT. If
Q303 VC02
OK, replace BJT
Q308 VC03
Field Effect Transistor (FET)
Q302 VC01
Q306 VC02
Q309 VC03
Check parts
FET
No
around FET. If
OK, replace FET
0V?
Yes
Check parts
BJT
No
around U300. If
OK, replace U300
>1.2V?
Yes
MAEPF-27398-O
April 15, 2002
6-15