Rx Rf Failure - Motorola APX 3000 Detailed Service Manual

Troubleshooting Charts: RX RF Failure
5.10 RX RF Failure – Page 1
Poor RX
sensitivity
or no RX
Inject a carrier wave with - 47dBm
into antenna port. Remove shield,
SH11. Use a spectrum analyzer
and high-impedance RF probe to
measure the IF signal at the input
side of C601 going to the Abacus.
IF Frequency =
109.65 MHz?
Is the IF signal level at the
input side of C601 about:
700: -50 dBm?
800: -55 dBm?
UHF1/UHF2: -50dBm?
VHF: -50 dBm?
Remove shield, SH8 and SH10. Measure RF levels
at the input side of L1117 and the input side of :
C2305 (for 7800 radios) or
C2605 (for UHF1/UHF2 radios) ,
C2705 (for VHF radios) ,
Compute the Harmonics Filter and Antenna Switch
Loss < 1.5
Measure RF levels at:
the input side of C2305 and pin 3 of U2302 (for
7800 radios) or
the input side of C2605 and pin 3 of U2602 (for
UHF1/UHF2 radios)
the input side of C2705 and pin 3 of U2702 (for
VHF radios)
Compute the 15dB step attenuator loss.
Note: The 15 dB step attenuator will be enabled.
Loss
<17dB?
Testing a
UHF1/UHF2/
VHF
Remove SH2.
Measure the LO
No power going into
the mixer, U507, at
the output side of
R525.
Yes
Yes
No
loss.
Remove shield SH8 and SH10.
No
Visual inspect the Harmonics Filter
dB? and Antenna Switch components and
replace parts if needed.
Yes
Check digital logic to the 15 dB
Step Attenuator and replace:
No U2302 (for 7800 radios) or
U2602 (for UHF1/UHF2 radios)
U2702 (for VHF radios).
Yes
No
Yes
2
Note: RF Test frequency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
VHF: 154.275MHz
800: 860.0625MHz
700: 769.0625MHz
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.
Is the LO power
around -3dBm?
Yes
1
if needed.
Testing a
7/800
radio?
Yes
No
Testing a
4
700
Yes
3
Check FGU
No and replace
U507 if
needed.
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