Troubleshooting Flow Chart For Vco - Motorola VHF2 Service Information

3-8
4.0

Troubleshooting Flow Chart for VCO

Low or no RF Signal
RX VCO
at TP1
Visual check
of board
3.3 DC at U201
Pin 14 & 18 OK?
4.5V DC at
U201 Pin 3 OK?
35mV DC at
U201 Pin 19
Are Q200
Base at 2.4V
Collector at 4.5V
Emitter at 1.7V
Check 9V at R230
Is RF available
at base of Q200
Check parts between
TP1 and Q200
NO
OK?
YES
Make sure U508 is working
NO
correctly and runner
between U508 Pin 1 and
U201 Pin 14 & 18 is OK
YES
Make sure Synthesizer is
NO
working correctly and runner
between U200 Pin 28 and
YES
NO
between U200 Pin 2
OK?
YES
NO
YES
YES
YES
NO
If all parts from U200 Pin 8
to Base of Q200 are OK,
NO
Correct
Problem
NO
NO
U201 Pin 3 is OK
Check runner
and U201 Pin 19
If all parts associated
with the pins are OK
replace U200
Power OK but
no modulation
TROUBLESHOOTING CHARTS
Low or no RF Signal
at input to PA
Visual check
of board
OK?
YES
5V DC at U201
Pin 14 & 18 OK?
YES
4.5V DC at
U201 Pin 3 OK?
YES
NO
4.8V DC at
U201 Pin 19
OK?
YES
Are U201 Pins
13 at 4.4V
15 at 1.1V
10 at 4.5V
16 at 1.9V
YES
NO
Is RF available
at C2060
YES
Check Transmiiter
Pre Driver
Audio =180mVrms
at "+" side of
D205
YES
NO
2.5VDC
at D205
YES
If R211 is Ok,
replace D205
TX VCO
If all parts
associated
NO
with the pins
are OK,
replace U201
If L216, C2071, C2070,
C2060 are okay
replace U201
NO
Replace R212
Replace R211