Troubleshooting Flow Chart For Vco - Motorola CDM Series Detailed Service Manual

Troubleshooting Flow Chart for VCO

4.0 Troubleshooting Flow Chart for VCO
Low or no RF Signal
RX VCO
at TP5003
Visual check
of board
OK?
4.5V DC
at U5301 Pin 14 & 18
OK ?
35mV DC at
U5301 Pin 19
OK?
Are Q5301
Base at 2.4V
Collector at 4.5V
Emitter at 1.7V
Is RF available
at base of Q5332
Are Q5332
Base at 0.7V
Collector at 4.5V
Emitter at 110mV
If all parts from collector
of Q5332 to TP5003 are
OK, Replace U5301
NO
Correct
Problem
YES
Make sure Synthesizer is
NO
working correctly and runner
between U5201 Pin 28 and
U5301 Pin 14 & 18 are OK
YES
NO Check runner
between U5201 Pin 2
and U5301 Pin 19
YES
NO
Replace Q5301
YES
NO
If all parts from U5301 Pin 8
to Base of Q5332 are OK,
replace U5301
YES
NO
If all parts associated
with the pins are OK,
replace Q5332
YES
Power OK but
no modulation
Low or no RF Signal
at input to PA
NO
Visual check
of board
OK?
YES
4.5V DC
NO
at U5301 Pin 14 &18
OK?
YES
NO
4.8V DC at
U5301 Pin 19
OK?
YES
Are Q5311
Base = 1.9V
Collector = 4.5V
Emitter = 1.3V
YES
Is RF available
NO
at U5401
Pin 16
YES
If all parts from U5301 Pin 10
U5401 Pin 16 are OK,
replace U5301
NO
Audio =180mVrms
Replace C5325
at "-" Side of
C5325
YES
NO
4.5VDC
Replace C5322
at CR5321
YES
If C5321 and R5321 are OK,
then replace CR5321
Section 6: 3-7
TX VCO
NO
Replace
Q5311
If R5361 and
L5361 are OK,
replace U5301
6881091C63-F