Troubleshooting Flow Chart For Vco - Motorola LB3 (42.0 - 50.0MHz) Service Information

Troubleshooting Flow Chart for VCO

4.0 Troubleshooting Flow Chart for VCO
RX - VCO
Low or no RF Signal
at U1051
Visual Check
of Board
OK?
YES
8.5V DC
at U1378
Pin 3
YES
<,1 V DC at
U1377 Pin 2
YES
8.5V DC AT
U1378 PIN 4
YES
Is RF
available at Base of
Q1304 ?
YES
Is RF
available at Base of
Q1305 ?
YES
Check parts between
U1051 and Q1305
NO
Make sure Synthesizer is
NO
working correctly and
runner between U1201 Pin
3 of U1377 & U1378.
Check runner
NO
between U1201 Pin 2
and U1377 Pin 2
NO
Make sure U1377 and U1378
are working correctly.
Troubleshoot
NO
Q1303
Oscillator Stage
Circuitry
Troubleshoot
NO
Q1304
Buffer Stage
Circuitry
Correct
Problem
Troubleshoot
Q1306
Oscillator Stage
Circuitry
Troubleshoot
Q1307
Buffer Stage
Circuitry
TX - VCO
Low or NO RF Signal
at Input to PA
Visual Check
NO
of Board
OK?
YES
NO
8.5V DC at
U1378 Pin 3
YES
NO
4.5V DC at
U1377 Pin 2
YES
NO
8.5V DC at
U1377 Pin 4
YES
Is RF
NO
available at Base of
Q1307 ?
YES
NO
Is RF
available at Base of
Q1308 ?
YES
Check parts between
U1401 and Q1308
3-5