M/A-Com 19D902797G5 Maintenance Manual - page 4
SYMPTOM
AREAS TO CHECK
INDICATIONS
1. No power or low power at An-
tenna 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. Measure 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.
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 the PA. Check connection
between PA and TX Synthesizer.
TX Synthesizer should deliver a minimum of
10 mW (10dBm) to the PA.
2. Check the logic or DC inputs to the PA from
the Interface Board through J201.
a. J201-PA KEY
b. J201-3 POWER SET
c. J201-6 13.8 VF
5 volts during transmit
4 volts to 8 volts (4 volts represents zero RF
power
13.8 Vdc
±
20%
3. Check the bias voltage on the base of Q5.
Voltage should be .73V nominal.
4. Check the bias voltage at module U2.
pin 2
pin 4
pin 6
pin 8
Note: There is no pin 3 on module U2. Pin 4
is the 3rd pin physically.
Voltages should be:
14-18V nominal
14-18V nominal
0.7V nominal
0.7V nominal
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 7 volts.
3. Check the power supply voltage on the
collector of Q5.
Voltage should be nominal 26.0 Vdc.
4. Check the bias voltage on the base of Q5.
Voltage should be .73V nominal.
5. Check the bias voltage at module U2.
pin 2
pin 4
pin 6
pin 8
Note: There is no pin 3 on module U2. Pin 4
is the 3rd pin physically.
Voltages should be:
14-18V nominal
14-18V nominal
0.7V nominal
0.7V nominal
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 mismatch 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
°
C to +60
°
C)
REFERENCE SYMBOL
READINGS
(volts DC)
SUPPLY VOLTAGE
A+
26.0 +5, - 20%
CONTROL VOLTAGE
Vctl
0-2V
FORWARD VOLTAGE
Vf
4-5V
REVERSE VOLTAGE
Vr
2-4V
POWER SENSE
J201-1
2.5 - 4V
PA KEY
J202-2
5V
POWER SET
J202-3
4 - 8V
13.8 VF
J201-6
13.8V
±
20%
800 MHz POWER AMPLIFIER VOLTAGE CHART
FREQUENCY
MHz
STANDARD
ADJUSTABLE
RANGE
851-870
100W, AFTER LOW PASS FILTER
10-100W, AFTER LOW PASS FILTER
RATED POWER FOR MASTR III 800 MHz BASE STATION
U3, U1
19A701789P4
Quad Op-Amp
U101
RYT1016155/1
IC DATA
LBI-39127H
3