Motorola APX 3000 Detailed Service Manual page 121

Troubleshooting Charts: RX RF Failure
RX RF Failure – Page 5
Remove shield, SH9.
Measure RF levels at the
RF switch, U402, and
compute switch loss.
800: output side of C402
& input side of R450.
Measure RF levels at the SAW
filter, FL401, and compute filter
800: output side of R450 and
output side of C412.
Measure RF levels at the RF
switch, U404, and compute
800: output side of C412 &
output side of C487.
Measure RF levels at LNA
and compute LNA gain.
800: input side of C423
and output side of R406.
Measure RF levels at the
RF switch, U403, and
compute switch loss.
800: output side of R406
& input side of R452.
Measure RF levels at the SAW
filter, FL402, and compute filter
800: output side of R452 and input
Measure RF levels at the RF
switch, U405, and compute
800: output side of R454 & input
Measure RF levels at LNA
and compute LNA gain.
800: input side of C430
and output side of R412.
Note: RF Test frequency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
4
VHF: 154.275MHz
700: 769.0625MHz
800: 860.0625MHz
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.
Check digital logic
No
to the RF switch
Loss < 2 dB?
and replace U402
if needed.
Yes
loss.
No
Replace
Loss < 2 dB?
FL401
Yes
switch loss.
Check digital logic
No
to the RF switch
Loss < 2 dB?
and replace U404
if needed.
Yes
No
Gain about
6
8 dB?
Yes
Check digital logic
No
to the RF switch
Loss < 1 dB?
and replace U403
if needed.
Yes
loss.
side of R454.
No
Replace
Loss < 3 dB?
FL402
Yes
switch loss.
side of C430.
Check digital logic
No
to the RF switch
Loss < 1 dB?
and replace U405
if needed.
Yes
No
Gain about
7
8 dB?
Yes
5
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