Rx Rf Failure - Motorola APX 7000 Detailed Service Manual

Troubleshooting Charts: RX RF Failure
5.15 RX RF Failure –Page 1
Poor RX
sensitivity or
no RX audio
Inject a carrier wave with -47dBm
into antenna port. Remove shield,
SH3. 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, SH12. IF level
at the mixer (output side of
series resistor, R511) about:
VHF: -44 dBm?
700: -48 dBm?
800: -45 dBm?
UHF1: -45 dBm?
UHF2: -46 dBm?
Remove shield, SH11.
Measure RF input level at the
antenna port (input side of
C1301).
RF level
about -49
dBm?
Remove shield, SH13.
Measure RF levels at the
input side of C1301 and the
input side of L1108,
compute RF switch, U1111
loss.
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
channel?
Switch to a VHF channel.
Measure RF levels at input
side of C1122 and at the
input side of C301. Compute
RF switch, U1122 loss.
Check digital
RF switch
logic to the No
RF switch loss < 1
and replace dB?
U1122
if needed.
2
Remove SH7.
Measure the LO
power going into the
mixer, U506, at the
output side of C528.
Yes
Testing a
UHF1/VHF or
No
UHF1 / 7/800 or
No
UHF1/UHF2 or
UHF2/VHF or
UHF2/ 7/800
Yes
radio?
Yes
1
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
Testing a
700
channel?
Yes
Yes
Switch to a 700 channel.
Measure RF levels at input
side of C1122 and at the
input side of C402. Compute
RF switch, U1122 loss.
Check digital
RF switch
logic to the No
loss < 2
RF switch
and replace dB?
U1122
Yes Yes
if needed.
3
Note
: RF Test frequency used:
VHF: 154.275 MHz
UHF1: 424.975 MHz
UHF2: 485.075 MHz
700: 769.0625 MHz
800: 860.0625 MHz
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 SH7.
Is the LO power
Measure the LO
= -5 dBm?
power going into the
mixer, U506, at the
output side of C599.
Yes
Visual
No
Replace
inspection
bad part
OK?
Yes
Bad antenna
connector.
Replace cable
assembly.
No No
Testing a
800
channel?
Yes
Switch to a 800 channel.
Measure RF levels at input
side of C1122 and at the
input side of C402. Compute
RF switch, U1122 loss.
Check digital Check digital
RF switch
logic to the No logic to the
RF switch loss < 2 RF switch
and replace dB? and replace
U1122 U1122
Yes
if needed. if needed.
4
Testing a
UHF1/VHF or
Check FGU and
No
UHF1 / 7/800 or No
replace U506 if
UHF1/UHF2
needed.
UHF2/VHF or
UHF2 / 7/800
radio?
Yes
Remove shield, SH1.
Check the polarity
of T505 and check
to see that all pins
are grounded.
Visually inspect windings.
Is
polarity correct,
all pins gounded
No
Replace T505
and
windings look
ok?
Yes
Check FGU and
replace U506 if
needed.
No
Testing a
UHF1
channel?
Yes
Switch to a UHF1 channel. Switch to a UHF2 channel.
Measure RF levels at input Measure RF levels at input
side of C1122 and at the side of C1122 and at the
input side of C2035. Compute input side of C1935. Compute
RF switch, U1122 loss. RF switch, U1122 loss.
Check digital
RF switch
No logic to the No
loss < 2 RF switch
dB? and replace
U1122
Yes
if needed.
15
5-33
Testing a
UHF2
channel?
Yes
RF switch
loss < 2
dB?
Yes
16