Motorola APX 1000 Detailed Service Manual page 140

5-42
RX RF Failure – Page 9
11
Measure control
voltage at U601
pin 38
Fvco too low?
7/800 & UHF1/UHF2:
<107.4 MHz
Yes
No
U601 Pin 38
= 5 Vdc?
Yes
Remove Abacus
2nd LO shield,
SH17 and inspect
second LO VCO.
Visual
examination
Yes
Replace
Varactor
VR602
(For reference only)
U601-38(Vdc) TP601 (MHz) Fvco
0.00
1.33
3.89
5.00
No
U601 Pin38 = 0
Vdc?
Yes
10
Repair
No
defects
102.70
107.40
111.90
Remove IF filter shield,
112.75
SH10. Check IF filter and
LC matching networks.
No
10
Note: RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075MHz
700: 769.0625MHz
800: 860.0625MHz
900: 938.0625MHz
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.
Troubleshooting Charts: RX RF Failure
12
No
Visual
inspection
OK?
Yes
Replace IF
filter, FL502.
Repair
Defects