Motorola APX 2000 - Page 794

5-38 Troubleshooting Charts: RX RF Failure
RX RF Failure – Page 9
(For reference only)
U601-38(Vdc) TP601 (MHz) Fvco
0.00 102.70
1.33 107.40
3.89 111.90
5.00 112.75
11
Measure control
voltage at U601
pin 38
Fvco too low?
7/800 & UHF1/UHF2:
<107.4 MHz
U601 Pin 38
= 5 Vdc?
U601 Pin38 = 0
Vdc?
10
10
Remove Abacus
2nd LO shield,
SH17 and inspect
second LO VCO.
Visual
examination
Repair
defects
Replace
Varactor
VR602
No
No
Yes
No
Yes
Yes
No
Yes
12
Remove IF filter shield,
SH10. Check IF filter and
LC matching networks.
Visual
inspection
OK?
Repair
Defects
Replace IF
filter, FL502.
No
Yes
Note: RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075MHz
700: 769.0625MHz
800: 860.0625MHz
Measured with a High Frequency Probe for
relative comparisons and troubleshooting only.
Actual S21 gain or loss may differ if the
test point is not 50 ohms.