Motorola GM640 Service Information - Page 24
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3-2
Troubleshooting Flow Chart for Receiver (Sheet 2 of 2)
1.1
B
Inject RF into J4401
IF Signal at
C3101?
No
RF
Signal at
T4051?
No
RF
Signal at
C4015?
No
RF
Signal at
C4009?
No or
weak RF
RF
Signal at
C4025?
No
Check harmonic filter
L4491-L4493, C4492, J4401
and ant.switch
D4471, D4472, L4472.
Trace IF signal
Yes
from C3101 to
Q3101. Check for
bad XTAL filter.
Yes
No
1st LO level
OK?
Locked?
Check T4051, T4052,
D4051, R4052, L4008.
Yes
Yes
Check filter between
C4015 & T4051.
Yes
Check RF amp (Q4003)
Stage.
Check filter between
Yes
C4025 & C4009.
Check tuning voltage
at R4060.
signal at Q3102
collector?
No
Check FGU
Check for
No
No
Check Supply Voltage
circuitry. Check Q0681,
U4211 and U0641.
Is
Yes
tuning voltage
OK?
No
Check U4501.
TROUBLESHOOTING CHARTS
IF
Yes
Before replacing
U3101, check
U3101 voltages.
Yes
A
5VDC
Yes
Is 9V3
A
present?
Check varactor filter.