Motorola APX 5000 Service Manual page 150

5-44
RX RF Failure – Page 10
13
Check Mixer:
Remove shield, SH5A. Check the
polarity of T503 and check to
see that all pins are grounded.
Visually inspect windings.
Is the polarity
correct and all pins
are gounded?
Yes
Measure the LO power going into the mixer, U506,
For VHF & 7/800 radio, at the output side of C599.
For UHF1 radio, at the output side of C528.
Is the LO power
= -5 dBm?
Yes
Remove shield, SH2. Check
the polarity of T504 and check
to see that all pins are
grounded. Visually inspect
windings.
Is the polarity
No
Replace
correct and all pins
T504
are gounded?
Yes
14
Note: RF Test frequency used:
VHF: 154.275MHz
UHF1: 424.975MHz
UHF2: 485.075 MHz
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.
No
Replace
T503
No
Testing a UHF radio?
Yes
Remove shield, SH7. Check
the polarity of T505 and check
to see that all pins are
grounded. Visually inspect
windings.
Is the polarity
correct and all pins
are gounded and the
No
windings look ok?
Yes
Check FGU and
replace U506 if
needed.
Replace
T505
14
Remove shields, SH2 &
SH5C. Measure IF level at
XTAL filter and compute
XTAL filter loss, non
ground side of C515 and
non ground side of C516.
Loss:
VHF: < 3 dB?
700: < 4 dB?
No
800: < 3 dB?
UHF1: < 3 dB?
UHF2: < 3 dB?
Yes
Measure RF levels at IF
Amplifier and compute
gain, input side of C519
& output side of R511.
No
Gain approximately 12dB?
Yes
No problem
found.
Check FGU and
replace U506 if
needed.
Troubleshooting Charts: RX RF Failure
12
Check LNA:
No
Check DC bias voltages
of Q503 at the base (pin
1) & collector (pin 3).
Is base voltage =
0.756 V?and
collector voltage =
1.560 V?
Yes
Check DC bias voltages of
Q501at the base (pin 2 or
5), collector (pin 3) and the
emitter (pin 4).
Is base voltage =
1.080 V? Collector
voltage = 0.756 V?
Emitter voltage = 1.583 V?
Yes
Check DC input line voltages
and visually inspect and
replace defective
components if needed.
No
Replace
Q503
No
Replace
Q501