Service manual

July 1, 2002 68P81076C25-C
4-68 Troubleshooting Procedures: Power Amplifier Procedures
3. Apply the required input power via adapter cable 30-80373B27 or equivalent. For this
application, non N-type connectors are acceptable.
4. With the applied control voltage initially at 0 V slowly increase the voltage until power out
equals 17 Watts (15-Watt radio) or 38 Watts (38-Watt radio) Power should rise smoothly with
control voltage once the turn-on threshold is reached. Control voltage should no exceed
11.0 V.
5. If 11.0 V does not produce 17 (or 38) Watts, then a failure exists in the power amplifier circuit.
6. Refer to the voltage chart (see Table 4-24). Measure the indicated voltages. If they are not
within the limits shown in the chart, then a failure exists in the PA assembly.
7. If the voltages in the chart are correct, verify that the injection is at least 75 mW. (See the
VCO troubleshooting section.)
8. If no failure is located from the previous checks troubleshoot the power control circuitry.
Table 4-23. DC Voltages and Input Power Chart
Test Keyed 9.4 V 9.6 V
CONTROL
VOLTAGE
DRIVE
POWER IN
(mW)
A+ .V
Transmit 9.4 9.6 See note
a
a. Set initially to zero. Increase value until power equals 17 wafts(15-Watt radio) or 38 Watts
(35-Watt radio) or 11.0 V maximum.
0.1 13.0
Receive 0 9.6 0 0 13.0
Table 4-24. Power Control DC Voltage Chart
LOCATION
RX MODE TX MODE
COMMENTS
LOW TYP HI LOW TYP HI
P0853
1 ——————
Key (no pin or wire)
2002.03.2
Control Voltage Limit
3 0 2.0 7.0 13.0
Drive Voltage
4 10.8 13.6 16.5 10.0 13.0 16.0
Current Sense +
5 0 0 0 9.2 9.4 9.8
Keyed 9.4
6 10.8 13.6 16.5 10.8 13.6 16.5
A+ to Command Board
70 1.2
Temp Sense (cutback begins at 3.3 V)
8 ——————
Key (no pin)
9 0 1.3 3.5 6.0
Forward Detect Voltage
10 10.8 13.8 16.5 10.8 13.6 16.5
A+ to Command Board
11 9.4 9.6 9.9 9.4 9.6 9.9
9.6-V Supply from Command Board
12 20.8 13.6 16.5 10.0 13.0 16.0
Current Sense - (voltage delta 150 mV)