Motorola APX 7000 - Advanced Features; Site Trunking Feature; Locking and Unlocking a Site

Troubleshooting Charts: RX RF Failure 5-35
RX RF Failure – Page 3
2
Remove shield, SH4.
Measure RF levels at first
preselector filter and
compute filter loss.
VHF: Input side of C301 &
output side of C307.
Loss < 2 dB?
Check components
and replace defective
parts.
No
Measure RF levels at LNA and
compute LNA gain.
UHF1/VHF and VHF / 7/800:
Input side of C311 & output side of R307.
UHF2/VHF: Input side of C311 &
output side of C329.
Gain about
18 dB?
Check LNA:
Check DC bias voltages of
U302 at the base (pin 1) &
collector (pin 3).
No
Is base voltage =
0.796 V? Collector
voltage = 1.563 V?
Replace
U302
Is base voltage = 1.017
V? Collector voltage =
0.796 V? Emitter
voltage = 1.566 V?
Replace
Q302
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
No
Yes
No
Yes
Measure RF levels at second
preselector filter and compute
filter loss.
VHF: input side of C318 & output
side of C326.
Loss < 6 dB?
Check components
and replace defective
parts.
No
Yes
Measure RF levels of the RF
switch, U501, at the input to the
mixer and compute loss.
VHF: output side of C502 and
input side of C511.
U501 loss
< 1 dB?
8
Yes
No
Yes
Yes
Check DC bias voltages of
Q302 at the base (pin 2 or
5), collector (pin 3) & emitter
(pin 4).
Check digital logic
to the RF switch
and replace U501 if
needed.
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.