Rx Rf Failure - Motorola APX 1000 Detailed Service Manual

5-30
5.11 RX RF Failure – Page 1
Poor RX
sensitivity or
no RX audio
Inject a carrier wave with -47dBm
into antenna port. Remove shield,
SH2. 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: -50 dBm?
VHF: -50 dBm?
Remove shield, SH7. Measure RF levels at
the input side of L1117 and the input side of:
C2705 (for VHF radios), C2605 (for UHF1/UHF2 radios),
or C2305 (for 700/800 radios).
Compute the Harmonics Filter and Antenna Switch loss.
Loss < 1.5 dB?
Measure RF levels at the input side of C2705 and pin 3 of U2702
(for VHF radios), C2605 and pin 3 of U2602 (for UHF1/UHF2 radios) or
the input side of C2305 and pin 3 of U2302 (for 700/800 MHz radios)
Compute the 15dB step attenuator U2602 or U2302 loss.
Note: The 15dB step attenuator will be enabled
Loss <17dB?
Testing a
UHF1/UHF2/
No
Yes
Yes
No
Remove shield SH8.
No
Visual inspect the Harmonics Filter and
Antenna Switch components and replace
parts if needed
Yes
Check digital logic to the 15dB Step
Attenuator and replace U2702
No
(for VHF radios), U2602
(for UHF1/UHF2 radios), or U2302
(for 700/800 MHz radios) if needed
Yes
No
VHF?
Yes
2
Note : RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075MHz
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.
Remove SH10.
Measure the LO
Is the LO power
power going into the
= -3 dBm?
mixer, U507, at the
output side of R525.
1
Testing a
700/800 MHz
radio?
Yes
No
Testing a
4
700?
Yes
3
Troubleshooting Charts: RX RF Failure
No
Yes
Check FGU and
replace U507 if
needed.