Motorola APX 3000 Detailed Service Manual

Troubleshooting Charts: RX RF Failure 5-27
5.10 RX RF Failure – Page 1
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?
Poor RX
sensitivity
or no RX
No No
Is the IF signal level at the
input side of C601 about:
700: -50 dBm?
800: -55 dBm?
UHF1/UHF2: -50dBm?
VHF: -50 dBm?
Yes
1
Yes
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.
Loss < 1.5
dB?
Remove shield SH8 and SH10.
Visual inspect the Harmonics Filter
and Antenna Switch components and
replace parts if needed.
No
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?
No
Yes
Yes
Testing a
7/800
radio?
Testing a
700
No
Yes
3
4
No
Check digital logic to the 15 dB
Step Attenuator and replace:
U2302 (for 7800 radios) or
U2602 (for UHF1/UHF2 radios)
U2702 (for VHF radios).
if needed.
Remove SH2.
Measure the LO
power going into
the mixer, U507, at
the output side of
R525.
Is the LO power
around -3dBm?
Yes
Note: RF Test frequency used:
UHF1: 424.975MHz
UHF2: 485.075MHz
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 FGU
and replace
U507 if
needed.
Yes
Testing a
UHF1/UHF2/
VHF
No
Yes
2

Motorola APX 3000 Specifications

General

Brand	Motorola
Model	APX 3000
Category	Two-Way Radio
Language	English