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

Troubleshooting Flow Chart for VCO

5.0 Troubleshooting Flow Chart for VCO
Low or no RF Signal
RX VCO
at TP3001
Visual check
of board
5V DC at U3301
Pin 14&18 OK ?
4.5V DC at
U3301 Pin 3 OK?
35mV DC at
U3301 Pin 19
Are Q3304
Base at 2.4V
Collector at 4.5V
Emitter at 1.7V
Are Q3301
Base at 0.7V
Collector at 4.5V
Emitter at 110mV
Is RF available
at base of Q3301
Check parts between
T3001 and Q3301
NO
OK?
YES
Make sure U3211 is working
NO
correctly and runner
between U3211 Pin 1 and
U3301 Pin 14 & 18 is OK
YES
Make sure Synthesizer is
NO
working correctly and runner
between U3201 Pin 28 and
YES
NO
between U3201 Pin 2
OK?
YES
NO
YES
NO
YES
NO
If all parts from U3301 Pin 8
to Base of Q3301 are OK,
YES
NO
Correct
Problem
NO
NO
U4301 Pin 3 is OK
Check runner
and U3301 Pin 19
If all parts associated
with the pins are OK,
replace Q3301
If all parts associated
with the pins are OK,
replace Q3301
replace U3301
Power OK but
no modulation
Low or no RF Signal
at input to PA
Visual check
of board
OK?
YES
5V DC at U3301
Pin 14&18 OK ?
YES
4.5V DC at
U3301 Pin 3 OK?
YES
NO
4.8V DC at
U3301 Pin 19
OK?
YES
Are U3301 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
YES
NO
Is RF available
at TP3401
YES
If all parts from TP3401 of
U3401 Pin 16 are OK,
replace U3401
Audio =180mVRMS
at "-" side of
D3362
YES
NO
2.5VDC
at D3362
YES
If C3362 and R3363 are OK,
then replace D3362
3-9
TX VCO
If all parts
associated
NO
with the pins
are OK,
replace U3301
If R3402 and
C3315 are OK,
replace U3301
NO
Replace R3364
Replace R3363