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Troubleshooting Procedures: Power Amplifier Procedures
4.11.3 UHF Range 2 (450–520 MHz) Band
Use this information, along with the theory of operation, to diagnose and isolate the cause of failures.
The principle tools needed to troubleshoot a circuit to the component level are the schematic and the
theory of operation.
In addition to the schematic and theory, you can use the troubleshooting flowcharts in
Troubleshooting Charts"
isolate problems.
Prior to troubleshooting, it is important to review the theory of operation including specific
precautions and troubleshooting methods. Because much of the radio's circuitry operates at
400 MHz, measurements must be taken carefully.
4.11.4 700–800 MHz Band
Use this information, along with the theory of operation, to diagnose and isolate the cause of failures.
The principle tools needed to troubleshoot a circuit to the component level are the schematic and the
theory of operation.
In addition to the schematic and theory, you can use the troubleshooting flowchart in
Troubleshooting Charts"
isolate problems.
Prior to troubleshooting, it is important to review the theory of operation including specific
precautions and troubleshooting methods. Because much of the radio's circuitry operates at
800 MHz, measurements must be taken carefully.
4.12 Power Amplifier Procedures
This section provides band-specific troubleshooting procedures for the RF power amplifier (RFPA).
4.12.1 VHF (136–174 MHz) Band
Use this information, along with the theory of operation, to diagnose and isolate the cause of failures.
The principle tools needed to troubleshoot a circuit to the component level are the schematic and the
theory of operation.
Prior to troubleshooting, be sure to review the theory of operation including any precautions and
troubleshooting methods.
4.12.1.1 50-Watt Power Amplifiers
In addition to the schematic and theory, this section includes troubleshooting information that will
help you test and check the circuits to localize and isolate problems.
4.12.1.2 General Troubleshooting and Repair Notes
Most of the common transmitter symptoms are caused by either failure of the power amplifier or a
failure in the control circuitry. The initial troubleshooting effort should be toward isolating the problem
to one of those two areas. If either the control voltage or keyed 9.4 V are zero, then the problem is
likely to be in the control circuit. If those voltages are present, then the problem is more likely in the
power amplifier circuit.
If for diagnostic reasons, a chip component needs to be removed to facilitate testing, such as a
series capacitor removed to allow for signal insertion, then the component(s) returned to the circuit
should be new parts. The application of a soldering iron to many chip components will tend to cause
leaching which could lead to failure.
6815854H01-A
that will guide you through a sequence of tests and checks designed to
that will guide you through a sequence of tests and checks designed to
4-33
"Chapter 5.
"Chapter 5.
June 15, 2005
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Table of Contents
Troubleshooting
