Motorola GM338

Troubleshooting Flow Chart for VCO 3-5
4.0 Troubleshooting Flow Chart for VCO
LOW OR NO RF SIGNAL
AT U1051
VISUAL CHECK
OF BOARD
OK?
8.5V DC AT
U1378 PIN 3
<,1 V DC AT
U1377 PIN 2
8.5V DC AT
U1378 PIN 4
CORRECT
PROBLEM
NO
YES
MAKE SURE SYNTHESIZER IS
WORKING CORRECTLY AND
RUNNER BETWEEN U1201 PIN
3 of U1377 & U1378.
CHECK RUNNER
BETWEEN U1201 PIN 2
AND U1377 PIN 2
IS RF AVAILABLE
AT BASE OF Q1304
TROUBLESHOOT Q1303
OSCILLATOR STAGE CIRCUITRY
IS RF AVAILABLE
CHECK PARTS BETWEEN U1051
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
RX VCO
LOW OR NO RF SIGNAL
AT INPUT TO PA
VISUAL CHECK
OF BOARD
OK?
8.5V DC AT
U1378 PIN 3
4.5V DC AT
U1377 PIN 2
8.5V DC AT
U1377 PIN 4
IS RF AVAILABLE
AT BASE OF Q1307
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
TX VCO
AND Q1305
AT BASE Q1305
TROUBLESHOOT Q1304
BUFFER STAGE CIRCUITRY
MAKE SURE U1377 AND U1378
ARE WORKING CORRECTLY.
IS RF AVAILABLE
AT BASE OF Q1308
A
B
NO
YES
CHECK PARTS BETWEEN
U1401 AND Q1308