M/A-Com 19D902797G1 Maintenance Manual - page 4
SYMPTOM
AREAS TO CHECK
INDICATIONS
1. No Power or low Power at
Antenna Port
1. Measure the transmitter output power
before the duplexer or antenna switch
(for
simplex
mode).
The presence of power at this port is an
indication of a defective duplexer,
switch, or cables.
2. Measuer the transmitter output power
before the low pass filter.
The presence of power at this port is an
indication of a defective filter or cables.
3. Measure the transmitter output power
before the optional isolator at the PA
output port.
The presence of power at this port is an
indication of a defective isolator or
cables.
2. No power at PA output port and
PA ALARM is OFF
1. Station is in receive mode.
3. No power at PA output port and
PA ALARM is ON.
1. No RF input to PA. Check connection
between PA and TX Synthesizer.
TX Synthesizer should deliver a
minimum of 10 mW (10 dBm) to the PA.
2. Check the logic or DC inputs to the PA
from the Interface Board through J201.
a. J201-2 PA KEY
5 volts during transmit
b. J201-3 POWER SET
4 volts to 8 volts (4 volts represents zero
RF power)
c. J201-6 13.8 VF
13.8 Vdc
±
20%
3. Defective PA
Replace PA
4. Low power at PA output port
and PA ALARM is OFF
1. Low RF input to PA from TX
Synthesizer.
Power should be a minimum of 10 mW
(10 dBM).
2. Check the voltage on J201-3
(POWER SET).
For nominal output power, this voltage
should be above 6 volts.
3. Check the power supply voltage on
the collector of Q101, Q102 and Q103.
Voltage should be nominal 13.4 Vdc.
4. One of the two final PA transistors
(Q102 or Q103 is defective.
Replace the defective transistor.
5. Low power at PA output port and
PA ALARM is ON.
1. Check for over temperature and/or a
high VSWR condition due to a mis-
match at the output port.
The power control circuit protects the
PA by cutting back the power. In case
of a mismatch, refer to symptom 1.
TROUBLESHOOTING GUIDE
PARAMETER
(50 OHM, -30
°
TO +60
°
C)
REFERENCE
SYMBOL
READINGS
(volts DC)
SUPPLY VOLTAGE
A+
13.4 V
±
20%
CONTROL VOLTAGE
Vct 1
0 - 12 V
FORWARD VOLTAGE
Vf
3 - 7 V
REVERSE VOLTAGE
Vr
2 - 6 V
POWER SENSE
J201-1
2.5 - 4 V
PA KEY
J201-2
5 V
POWER SET
J201-3
4 - 8 V
13.8 VF
J201-6
13.8 V
±
20%
VHF POWER AMPLIFIER VOLTAGE CHART
REFERENCE
SYMBOL
@ 136 MHz
(volts DC)
@ 150 MHz
(volts DC)
@ 162 MHz
(volts DC)
@ 174 MHz
(volts DC)
Vct1
7 - 10 V
6 - 8 V
4 - 6 V
4 - 6 V
Vf
5 - 7 V
5 - 7 V
5 - 7 V
5 - 7 V
Vr
2 - 3 V
2 - 3 V
2 - 3 V
2 - 3 V
J201-1
2.5 - 4 V
2.5 - 4 V
2.5 - 4 V
2.5 - 4 V
J201-3
6 - 8 V
6 - 8 V
6 - 8 V
6 - 8 V
J201-6
13.4 V
13.4 V
13.4 V
13.4 V
VHF POWER AMPLIFIER TYPICAL VOLTAGE READINGS
(50 ohm, room temperature, 13.4 Vdc supply voltage, and 110 watt output)
RATED POWER FOR MASTR III VHF BASE STATION
STANDARD
WITH
DUPLEXER
WITH
ISOLATOR
WITH DUPLEXER
AND ISOLATOR
110W
75W
95W
70W
LBI-38531G
3