IS THERE A 30mV p-p SIGNAL AT
2x XTAL FREQUENCY?
THEN INJECTION
OK
MIXER PROBLEM. CHECK BIASING OF
TR103 (R106, R105, R104, C111, C110,
TR103)
C1
CONNECT A SCOPE WITH A x10
PROBE TO THE EMITTER OF
TR102. IS THERE ≈700mV p-p AT
THE XTAL FREQUENCY?
LOCAL OSCILLATOR STOPPED.
CHECK BIASING OF TR102 (XL101,
C115, C116, R108, R107, R109,
TR102)
LOCAL OSCILLATOR
DOUBLER/INJECTION PROBLEM.
CHECK BIASING OF L103, C117, C114,
C109, C112, C113
REMOVE R107, TO DISABLE THE LOCAL
OSCILLATOR. APPLY -30dBm TO SK102.
USING AN RF MILLIVOLTMETER
MEASURE TR101 COLLECTOR
IS IT ≈100mV?
CAN THE LEVEL BE PEAKED WITH
L101 TO GIVE ≈100mV?
RF AMP PROBLEM. CHECK BIASING ON
TR101 (L101, C101, C102, C103, R103,
C108, R102, R101, C120, C106, C118,
TR101)
NO
YES
NO
YES
YES
YES
NO
NO
RPR 550IS Series
TM1188 Issue 1 Page 5 - 13
Figure 4: Fault-Finding Guide
(Continued)
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