Poor Rx Sensitivity Or No Rx Audio (700-800 Mhz)-Part 2 Of 2 - Motorola ASTRO XTL 1500 Detailed Service Manual

Troubleshooting Charts: Flowcharts
5.6.34 Poor RX Sensitivity or No RX Audio (700–800 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 TP6253.
<~1dB Loss
relative to Antenna
switch?
Yes
Check LNA Input
(U6250) Pin 3. RF
_
Level:<~2.5dB Loss
from TP6253
Yes
Check
LNA Output
TP6250. RF Level:
~16dB gain from
U6250 Pin
3?
Yes
Check
Mixer Input,
TP6251. RF Level:
_
<~2.5dB Loss from
TP6250?
Yes
Check
Mixer Output,
TP6252. Freq: 73.35MHz
RF Level: <~7db
Loss from
TP6251
RF Level at
_
TP6252<~7db
loss from TP6251
Yes
Go to IF Section
Troubleshooting
flowchart
Figure 5-34. Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 2 of 2
6815854H01-A
3kHz FM Deviation
1kHz Audio tone
Amplitude: 47dBm
Check Output
Network (ON)
No
troubleshooting
flowchart of
Transceiver
Check filter switching
No
table or proper voltages.
Visually inspect filters
Check bias
No
voltage at Pin 1
of U6250 for 5V
Replace
part
Check filter switching
No
table for proper voltages.
Visually inspect filters
Is Output Freq
_ at 73.35MHz?
Check RF level at
No
Mixer LO injection
port. (U6251
Pin 3 side 1)
Yes
Check Pin 3 on U6251
No
for correct LO frequency
(based on your
Receiving signal)
Yes
RF level
at ~14dBm
Check Receiver
No
VCO troubleshooting
flowchart
(LO injection section)
MAEPF-27874-O
June 15, 2005
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