Motorola ASTRO SPECTRA Service Manual page 139

Basic Troubleshooting: Receiver Troubleshooting
Symptom
RF Sensitivity
Poor
Radio Will Not
Squelch
Radio Will Not
Turn Off
Excessive
Noise in
Fading
Conditions
6881076C20-E
Table 9-6. Receiver Troubleshooting Chart (Continued)
Possible Cause
Synthesizer Not On
Frequency/Working
Antenna Switch
(Amplifier Board)
Receiver Front-End
Assembly or VCO
Board
RF Board
Codeplug
On/Off Switch (Control
Head)
Command Board
Check Programming for
Correct Bandwidth
Correction or Test (Measurements Taken
at Room Temperature)
Check local oscillator frequency.
If off by more than 250 Hz, then go to the
Synthesizer Troubleshooting Chart (
Check insertion loss from antenna connector to
Rx front end coax from the PA.
If loss is less than 1.8 dB, then the problem is in
the transceiver housing.
1. Measure the gain of the front end assembly by
injecting a signal at the desired receive frequency
and measuring the output level at 109.65 MHz.
Net conversion gain should be >8 dB.
2. If conversion gain is <8 dB, then check the dc
supply voltage fed into the front end on the center
conductor of the output coax to the RF board.
If it is less than 9.4 Vdc, check the RF board.
3. Check the injection level from the VCO board.
If it is less than +2 dBm, then replace the VCO
board.
If injection is OK, then replace the receiver front-
end assembly.
Using a TEK-10 probe, check the sensitivity into
the RF board @ 109.65 MHz.
If sensitivity is worse than -118.5 dBm for 12 dB
SINAD, replace the RF board.
Check the offending channel for spurious activity
by monitoring with a known-good radio or service
monitor.
If possible, remove the offending source
(computer, etc.).
If not, increase the squelch level using the
appropriate radio programming software.
Check for SWB+ pin 31 P502 on the command
board.
If SWB+ is not there, check for SWB+ at pin 21 of
P502 on the command board.
Replace the control head.
Does SWB+ on pin 31 of P502 switch on and off
as the control head switch is operated?
If so, replace the command board.
Reprogram codeplug with correct bandwidth.
9-11
page 9-12
).
February 3, 2003