Motorola APX 7000 Detailed Service Manual page 147

Troubleshooting Charts: RX RF Failure
RX RF Failure – Page 11
Remove shield, SH4.
Measure RF levels at first
preselector filter and
compute filter loss.
UHF1: Input side of C2035
& output side of C2039.
Loss < 3.5
dB?
Measure RF levels at LNA
and compute LNA gain.
UHF1: Input side of C2033
and output side of C2044.
Gain about
18 dB?
Measure RF levels at second
preselector filter and compute
filter loss.
UHF1: input side of C2059 &
output side of C2061.
Loss < 5
dB?
Remove shield, SH7. Measure
RF levels at the filter and
compute filter loss. Output
side of C2061 and output side
of C510.
Filter Loss
< 3 dB?
Measure RF levels of the RF
switch, U501, at the input to the
mixer and compute loss.
UHF1: output side of C510 and
input side of C511.
U501 loss
< 1 dB?
15
Check components
No
and replace defective
Autotune the radio.
Yes
No
Yes
Check components
No
and replace defective
Autotune the radio.
Yes
Visually inspect
No
and replace
components if
necessary.
Yes
Check digital logic
to the RF switch
No
and replace U501 if
needed.
Yes
8
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.
parts.
Check DC bias voltages of
U2032 at the base (pin 1) &
collector (pin 3).
Is base voltage =
0.787 V? Collector
voltage = 1.56 V?
parts.
Check DC bias voltages of
Q2022 at the base (pin 2 or
5), collector (pin 3) & emitter
Is base voltage = 1.022
V? Collector voltage =
0.787 V? Emitter
voltage = 1.561 V?
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
Check LNA:
No
Yes
(pin 4).
No
Yes
5-43
Replace
U2032
Replace
Q2022