Ericsson LBI-31511B, Maintenance Manual, Page: 6 / 18

TROUBLESHOOTING PROCEDURE
NOTE
Reg5 Vdc and +9 Vdc can be opened by P701 thru P705 to facilitate troubleshooting.
POWER AMPL METERING J1
PA JACK READINGS
METER
READING
PROBABLE CAUSE
80, 90
100W
35, 40
50W
65,
75W
TEST
POS.
METERING
POINT
FUNCTION
MEASURED
SCALE
TYPICAL
READING
TYPICAL
READING
TYPICAL
READING
HIGH LOW
A J1-10 RF DRIVE 0-1 V 0.5 V 0.5 V 0.5V
L o w e x c i t e r o u t p u t .
Realign or repair exciter.
B J1-9 CONTROL
VOLTAGE
0-15V 4 V 4.5 V 7.5V
L o w e x c i t e r
output High exciter output.
C J1-8 TX A+ 0-15V 12.5V 12.5V 12.5V
Excessive voltage drop
in power cable.
E J1-6 PA
CURRENT
0-30A 15 A --- 11A
R F o u t p u t
e x c e s s i v e l y
high. Be sure
a n t e n n a i s
p r o p e r l y
matched to 50
ohms. RF output low.
F J1-5 DRIVER
CURRENT
0-15A 5 A 8 A 4A 1 0 0 W A T T
PA C h e c k
A 1 Q 5 a n d
A 1 Q 6 . B e
s ur e a ntenna
i s p r o p e r l y
matched to 50
ohms. 100 WATT PA A1Q5
a n d A 1 Q 6 h a v e
excessive gain. RF gain.
RF output set too low.
40 WATT PA
R F o u t p u t
p o w e r i s
excessive. Be
s ur e a ntenna
i s p r o p e r l y
matched to 50
ohms. 40 WATT PA Low RF
output.
(Cont.)
PA QUICK CHECKS
–
Connect red system metering plug to J602, system metering.
–
Connect black plug of GE Test Set of RF Metering jack J1 of PA. Set polarity to "+" and voltage range to the 1 volt
position (Test 1).
(Cont.)
PA TROUBLESHOOTING PROCEDURE
When troubleshooting the transmitter check for typical meter readings for the exciter, J101, and the power amplifier JACK,
J1. Typical readings for the various test positions and test points are given in the charts below.
SYMPTOM PROCEDURE ANALYSIS
Little or No
RF Output Key transmitter and check J1-10 (Pos A) for +0.5
V (exciter output). Refer to Schematic Diagram and verify voltage
readings.
Unkey transmitter and check Q105-C for +9.0
Vdc. 9.0 volt supply. Check R124 and L117.
Check DC voltages on Q101-Q105. If voltages are incorrect, check L103, L106, L110,
L112, L117 and all resistors for each stage. Check
R106, R110, R114, R118, R119 and R124. Check
Q101-Q105. Replace components if defective.
Disconnect P102 on Exciter and measure RF
output of synthesizer. No RF present: see Synthesizer Troubleshooting
Procedure.
Key transmitter and monitor voltage at J101-9
(Pos B Tripler). Voltage should increase. RF present: reconnect P102 and proceed to next step.
Monitor J101-8 (Pos C) and key transmitter.
Voltage should increase. If voltage does not increase check Q116-Q118, L106
and associated components.
Disconnect P103 on exciter and measure RF
output power from exciter. Should be 0.5 watts or
more. If voltage does not increase, check Q103, Q104 and
associated components. Check D101 and associated
metering circuitry. Finally, check both helical filters.
If exciter output is low, check Q105 and associated
circuitry. Also check 2nd helical filter including L114
and L115. Retune exciter if needed.
If output power is correct be sure P101 is soldered
securely and that it mates properly with the contact on
the power amplifier.
LBI-31511 LBI-31511
5