Poor Rx Sensitivity Or No Rx Audio (700-800 Mhz)-Part 1 Of 2 - Motorola ASTRO Digital XTL 5000 Detailed Service Manual

Troubleshooting Charts: Flowcharts
5.6.33 Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 1 of 2
Poor Rx
Sensitivity or no
Rx audio
Yes
Measure Transceiver
Sinad by injection
signal at antenna port
Yes
Sinad
< - 119.1dBm?
No
Check RF level at
Mixer LO injection port
(U6251 Pin 3 side 1)
RF level
at ~ 14dBm?
Yes
Check RX front-end
filter switching
voltage Table
Good?
Yes
1
Figure 5-35. Poor RX Sensitivity or No RX Audio (700–800 MHz)—Part 1 of 2
6881096C74-B
3kHz FM Deviation
1kHz Audio tone
Receiver
Yes
is working
properly
Check Receiver
VCO troubleshooting
No
flowchart
(LO injection section)
Check Q6350,
Q6251, Q6252,
No
Q6253, Q6254
and make any
necessary repairs
RX Switching Voltages
Receiving at
Test Points
700MHz Band
TP6254
0V
TP6255, 57,
59, 61
7.6V
TP6256, 58,
2V
60, 62
LNA U6250
5V at Pin 1
MAEPF-27875-O
5-47
Receiving at
800MHz Band
3V
4V
7.6V
May 25, 2005