Troubleshooting Flow Chart For Vco - Motorola 6864115B62-C Detailed Service Manual

3-8
5.0

Troubleshooting Flow Chart for VCO

Low or no RF Signal
RX VCO
at TP4003
Visual check
of board
4.5V DC
at U4301 Pin 14 & 18
35mV DC at
U4301 Pin 19
Are Q4301
Base at 2.4V
Collector at 4.5V
Emitter at 1.7V
Is RF available
at base of Q4332
Are Q4332
Base at 0.7V
Collector at 4.5V
Emitter at 110mV
If all parts from collector
of Q4332 to TP4003 are
OK, Replace Q4332
NO
OK?
YES
Make sure Synthesizer is
NO
working correctly and runner
between U4201 Pin 28 and
OK ?
U4301 Pin 14 & and is OK
YES
NO
between U4201 Pin 2
OK?
YES
NO
YES
NO
If all parts from U4301 Pin 8
to Base of Q4332 are OK,
YES
NO
YES
Power OK but
no modulation
NO
Correct
Problem
NO
Check runner
and U4301 Pin 19
Replace Q4301
replace U4301
If all parts associated
with the pins are OK,
replace Q4332
Audio =180mVRMS
If C4321 and R4321 are OK,
TROUBLESHOOTING CHARTS
Low or no RF Signal
at input to PA
Visual check
of board
OK?
YES
4.5V DC
at U4301 Pin 14&18
OK ?
YES
NO
4.8V DC at
U4301 Pin 19
OK?
YES
Are U4301 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
YES
NO
Is RF available
at C4402
YES
Check parts from
R4402 to U4401 Pin16
NO
Replace C4325
at "-" S ide of
C4325
YES
NO
4.5VDC
Replace C4322
at CR4321
YES
then replace CR4321
TX VCO
If all parts
associated
NO
with the pins
are OK,
replace U4301
If parts between
R4402 & U4301 Pin10
are OK, replace U4301