Rx Rf Failure - Motorola APX 5000 Service Manual

Troubleshooting Charts: RX RF Failure
5.18 RX RF Failure – Page 1
Poor RX
sensitivity or
no RX audio
Inject a carrier wave with -47dBm
into antenna port. Remove shield,
SH6A. 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?
Remove shield, SH5A. IF level
at the mixer (output side of
series resistor, R511) about:
VHF: -44 dBm?
UHF1: -45 dBm?
UHF2: -45 dBm?
700: -48 dBm?
800: -45 dBm?
Remove shield, SH11.
Measure RF input level at the
antenna port (input side of
C1301).
RF level
about -49
dBm?
Remove shield, SH13 for 700/800
or SH10 for UHF1 and UHF2.
Measure RF levels at the input side
of C1301 and the input side of L1108,
compute RF switch, U1111 loss.
(Skip if VHF).
RF switch
loss ~ 1 dB?
Measure RF levels at the output side of L1108 and
the input side of C1122, compute RF switch, U1102
loss.
Note: The 15 dB attenuator in the RF switch will be
enabled.
RF switch
loss <17dB?
Testing a
VHF
radio?
Measure RF level at
output side of C1149
and Pin 3 on U1149.
Loss ~ 15 dB?
Remove SH7.
Measure the LO
power going into the
mixer, U506, at the
output side of C528.
Yes
No
Testing a
UHF1 or
UHF2?
Yes
Yes
No
Inspect coaxial
No
antenna connector
and cable
assembly
Yes
Check digital logic
No
to the RF switch
and replace U1111
if needed.
Yes
Check digital logic
No
to the RF switch
and replace U1102
if needed.
Yes
No
Yes
Check logic on
No
attenuator U1149
and replace
if needed.
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 impedance probe for relative comparisons and troubleshooting only.
Actual S21 gain or loss may differ if the test point is not 50 ohms.
Remove SH5A.
No
Measure the LO
Is the LO power
power going into the
= -5 dBm?
mixer, U506, at the
output side of C599.
1
Visual
No
Replace
inspection
bad part
OK?
Yes
Bad antenna
connector.
Replace cable
assembly.
No
Testing a
7/800
radio?
Yes
Testing a
No
700
4
channel?
3
No
Testing a No
UHF1 or
UHF2?
Yes
Yes
Remove shield, SH7.
Check the polarity
of T505 and check
to see that all pins
are grounded.
Visually inspect
windings
Yes
Is
polarity correct,
all pins gounded
and
windings look ok?
Yes
Check FGU and
replace U506 if
needed.
Testing a
UHF1 or UHF2
radio?
Yes
15
5-35
Check FGU and
replace U506 if
needed.
No
Replace T505