Motorola MTX series - Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)

8-52 Maintenance: 900 MHz Troubleshooting Charts
8.17.3 Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)
Bad SINAD.
Bad 20dB Quieting.
No Recovered Audio
START
Audio at
pin 27 of
U351?
Check Controller.
Ye s
No
Spray or inject 1st IF into XTAL
Filter.
IF Freq: 109.65 MHz
Audio heard?
B
Ye s
No
Check 2nd LO Control
Voltage at R365
VCO locked?
B
Ye s
16.8 MHz
check at pin
21 of U351?
Activity
on U351
pin 19?
Check FGU
No
No
A
A
Ye s
Check Q350 bias cir-
cuitry for faults
Rotate Freq. Knob
Check controller
Before replacing U351, check
2nd VCO Q350. Check VCO O/P
level, C385, C387
Ye s
No