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

5-18

5.11 VCO TX/RX Unlock

VCO TX/RX
unlock
Sniff: Using an inductive field probe
"Sniff"
frequency near
VCO shield
No
Frequency
5V at TP3?
detected?
Yes
Check parts
Check control
voltage at around U2. If
TP243 OK, replace U2
Check if VCO
<0.6Vdc
No
>11.0Vdc or
is locked using
drifting?
spectrum analyzer
Yes
Check parts
No
around U202. If VCO locked?
OK, replace U202
Check
VOCON board
October 14, 2003
as an antenna to measure
frequency. Place the probe
approximately 1/2 inch away
from components to be sniffed.
Check parts
No
around U1. If
OK, replace U2
Yes
No
3V at TP5?
Yes
Remove
VCO shield
Is unit
VHF?
Yes
No
Field Effect Transistor (FET)
Aux.
line 1 (2,4)
is high?
No
Bi-polar Transistor (BJT)
Q301 VC01
Q303 VC02
Q308 VC03
Troubleshooting Charts: VCO TX/RX Unlock
Aux. line
Yes Yes
3 high for TX
or low for RX
(VHF)?
No
Q302 VC01
Q306 VC02
Q309 VC03
FET
No
Yes
drain voltage
0V?
Yes
BJT
No
emitter voltage
OK, replace U300
>1.2V?
Yes
Check parts
around BJT. If
OK, replace BJT
Is pin
Remove
19 of VCOBIC No
VCO buffer
low for RX and
shield (SH302)
4.5 for TX?
Yes
Check parts
Check parts
around U302.
around Q301. If
If OK, replace
OK, replace Q301
Q302
Check parts
around FET. If
OK, replace FET
Check parts
around U300. If
MAEPF-27398-A
6881094C31-C