Poor Rx Sensitivity Or No Rx Audio (380–470 Mhz And 450–520 Mhz)—Part 2 Of 2 - Motorola ASTRO XTL 1500 Detailed Service Manual

5-26
5.6.15 Poor RX Sensitivity or No RX Audio (380–470 MHz and 450–520 MHz)—Part 2
of 2
1
Inject a standard FM test
signal into the antenna port.
Use a spectrum analyzer and
high-impedance RF probe to
measure the signal at TP5301
<~1dB Loss
relative to Antenna
switch?
Yes
Check preselector Input
at C5304. RF Level
at TP5301 should be
-0.5dB without pre-amp
and +11dB with pre-amp.
Yes
Check preselector
insertion loss is
~2.0dB.
Yes
Check
U5302 LNA Output
at C5320. RF Level:
~15dB gain at
C5312?
Yes
Check
Mixer Input,
TP5303. RF Level:
_
<~2.5dB Loss at
C5320?
Yes
Check
Mixer Output,
TP5304. Freq: 109.65MHz
_
RF Level: <~7db
Loss from
TP5303
_
RF Level at
TP5304<~7db
loss from TP5303
Yes
Figure 5-17. Poor RX Sensitivity or No RX Audio (380–470 MHz and 450–520 MHz)—Part 2 of 2
June 15, 2005
3kHz FM Deviation
1kHz Audio tone
Amplitude: -47dBm
Check Output
Network (ON)
No
troubleshooting
flowchart of
Transceiver
No Check Q5252 LNA and
its bypass switch.
No
Check preselector and
tuning voltage.
Check bias
No
voltage at
L5294 for 5V
Yes
Replace
part
No
Fix Image filter.
Is Output Freq
at 109.65MHz?
Yes
No
Check RF level at
Mixer LO injection
port at R5388.
Troubleshooting Charts: Flowcharts
Check at R5388
No
for correct LO frequency
(based on your
Receiving signal
+109.65MHz)
Check Receiver
No
RF level VCO troubleshooting
at +24dBm
(LO injection section)
flowchart
6815854H01-A