Motorola Astro APX 3000, Detailed Service Manual

Page: 120 / 474

5-30 Troubleshooting Charts: RX RF Failure
RX RF Failure – Page 4
3
Remove shield, SH9.
Measure RF levels at the
RF switch, U402, and
compute switch loss.
700: output side of C402
& input side of R451.
Loss < 1 dB?
No
Measure RF levels at the SAW
f ilter, FL401, and compute f ilter
loss.
700: Output side of R451 and
output side of C413.
Loss < 3 dB?
No
Replace
FL401
Measure RF levels at the RF
switch, U404, and compute
switch loss.
700: output side of C413 &
output side of C487.
Loss < 1 dB?
No
Yes
Measure RF levels at LNA
and compute LNA gain.
700: input side of C423
and output side of R406.
Gain about
10 dB?
Yes
No
Yes
Yes
Measure RF levels at the
RF switch, U403, and
compute switch loss.
700: output side of R406
& input side of R453.
Loss < 1 dB?
No
Measure RF levels at the SAW
f ilter, FL402, and compute f ilter
loss.
700: Output side of R453 and input
side of R455.
Loss < 6 dB?
No
Measure RF levels at the RF
switch, U405, and compute
switch loss.
700: output side of R455 & input
side of C430.
Loss < 1 dB?
No
Yes
Measure RF levels at LNA
and compute LNA gain.
700: input side of C430
and output side of R412.
Gain about
10 dB?
Yes
No
Yes
Yes
Replace
FL402
5
7
6
Check digital logic
to the RF switch
and replace U403
if needed.
Check digital logic
to the RF switch
and replace U405
if needed.
Check digital logic
to the RF switch
and replace U402
if needed.
Check digital logic
to the RF switch
and replace U404
if needed.
Note: RF Test f requency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
VHF: 154.275MHz
700: 769.0625MHz
800: 860.0625MHz
Measured with a High Frequency Probe f or relative comparisons and troubleshooting
only. Actual S21 gain or loss may dif f er if the test point is not 50 ohms.