Motorola Professional GP680 Service Information - Page 23

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Motorola Professional GP680 Service Information
1.0

Troubleshooting Flow Chart for Receiver (Sheet 1 of 2)

A
START
Bad SINAD
Bad 20dB Quieting
No Recovered Audio
A
udio
at pin 27 of
U301?
No
Spray of inject 1st IF into
XTAL Filter
IF Freq: 45.1MHz
Yes
Audio
B
heard?
No
Check 2nd LO Control Voltage at C363
Yes
VCO
B
locked?
No
16.8 MHz
Yes
at pin 22
U301?
No
Check FGU

TROUBLESHOOTING CHARTS

Yes
Check Controller
Before replacing U301, check 2nd
VCO Q320. Check VCO O/P level,
Chapter 3
A
Check Q320 bias
circuitry for faults.
Rotate Freq. Knob
Activity
No
on U301
LVZIF_SEL
pin?
Yes
Check controller
C351, C352.