Motorola APX 3000 Detailed Service Manual page 119
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Also See for APX 3000:
- Basic service manual (144 pages) ,
- User manual (104 pages) ,
- Manual (59 pages)
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Troubleshooting Charts: RX RF Failure
RX RF Failure – Page 3
2
Remove shield, SH9.
Measure RF levels at first
preselector filter and
compute filter loss.
UHF1/UHF2: Input side of
C1935 & output side of C1939.
VHF: Input side of C330
& output side of C339.
Loss < 3 dB?
Yes
Measure RF levels at LNA
and compute LNA gain.
UHF1/UHF2: Input side of
C1931 and output side of C1936.
VHF: Input side of C339 and
output side of C360.
Gain about
15 dB?
Yes
Measure RF levels at second
preselector filter and compute
filter loss.
UHF1/UHF2: input side of
C1959 & output side of C1961.
VHF: input side of C345 & output
side of C357.
Loss < 4 dB?
Yes
5
Note: RF Test frequency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
VHF: Input side of C330 & output side of C339.
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 components
No
and replace
defective parts.
Autotune the radio.
No
Check components
No
and replace
defective parts.
Autotune the radio.
Check LNA:
Check DC bias voltages of
UHF1/UHF2: U1932 at the
base (pin 1) & collector (pin 3).
VHF: U304 at the base
(pin 1) & collector (pin 3).
Is base voltage =
0.787 V?
Collector voltage =
1.56 V?
Yes
Check DC bias voltages of
UHF1/UHF2: Q1922 at the base
(pin 2 or 5), collector (pin 3)
& emitter (pin 4).
VHF: Q303 at the base
(pin 2 or 5), collector (pin 3)
& emitter (pin 4).
Is base voltage =
1.022 V? Collector
voltage = 0.787 V?
Emitter voltage =
1.561 V?
Yes
Check DC input line
voltages and visually
inspect and replace
defective components if
needed.
Replace
No
UHF1/UHF2: U1932
VHF: U304
No
Replace
UHF1/UHF2: Q1922
VHF: Q303
5-29
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Troubleshooting
