Troubleshooting Charts: RX RF Failure 5-41
RX RF Failure – Page 9
TP602(Vdc) TP601 (MHz) Fvco
0.00 102.70
1.47 107.40
4.16 111.90
5.00 112.80
11
Measure control 
voltage at TP602
Fvco too low?
VHF,7/800,UHF1 
& UHF2:
<107.4 MHz
TP602 = 
5 Vdc?
TP602 = 0 
Vdc?
10
10
Remove Abacus 
shield, SH3, and 
inspect second LO 
VCO.
Visual 
examination 
OK?
Repair 
defects
Replace 
Varactor 
VR602
No
No
Yes
No
Yes
Yes
No
Yes
12
Remove IF filter shield, 
SH2.  Check IF filter and 
LC matching networks.
Visual 
inspection 
OK?
Repair 
Defects
Replace IF 
filter, FL501.
No
Yes
Note: RF Test frequency used:
VHF:   154.275 MHz
UHF1: 424.975 MHz
UHF2: 485.075 MHz
700:    769.0625 MHz
800:    860.0625 MHz
Measured with a high impedance probe for 
relative comparisons and troubleshooting only.
Actual S21 gain or loss may differ if the 
test point is not 50 ohms.