*TM-1 1-5821-284-34
CHAPTER 4
GENERAL SUPPORT MAINTENANCE
Section I. GENERAL
(5) Before testing or troubleshooting,
4-1.
Scope of General Support Maintenance
check the source voltage of the power supply circuits.
a. General Support Maintenance General
Abnormal supply voltages often affect frequency any
support maintenance supplement direct support
stability characteristics and the output or gain of the
maintenance, and encompass all maintenance
circuits.
categories. The troubleshooting procedures in this
b. When
troubleshooting
transistorized
chapter are prepared for use by general support
circuits, observe the following:
maintenance shops to locate and repair a malfunctioning
(1) In a transistorized amplifier, any
circuit.
They are used in conjunction with the
change in the output circuit of one stage can affect all
Performance Standards of chapter 5 Overhaul tasks can
preceding stages; therefore, any deviation in the
be effected using the normally authorized tools and test
operating characteristics of a certain stage can be
equipment.
reflected back to affect the operation of the preceding
b. Depot Repair Depot repair is covered In
stages
DMWR 11-5821-284.
(2) Common-emitter
transistorized
4-2.
Test Equipment and Additional Equipment
amplifiers have a 1800 phase shift between the input and
Required
output voltage; however, there will be no phase shift
In addition to the test equipment authorized for direct
between the input and output signals if the base is short-
support maintenance (para 3-2), the multimeter ME-
circulated to the collector.
26B/U is required for measurement of ac and dc
(3) During normal operation of a common-
voltages and resistance.
emitter transistor amplifier, the base voltage should be
4-3.
General Precautions
slightly higher than the emitter voltage An open circuit
a. When servicing the antenna components
between the base and emitter will produce a base
observe the following precautions:
voltage con-siderably greater than normal and an emitter
(1) Connect a suitable ground to the
voltage near ground potential
antenna. This is a safety precaution and also prevents
(4) An unusually high dc collector voltage
abnormal electrical effects caused by the absence of a
can be caused by an open emitter circuit, an open
ground connection.
collector circuit, or a short circuit between the base and
(2) Remove all power from the antenna
emitter An open circuit between the base and emitter
and from the component under test before contacting
may also cause an unusually high collector voltage.
any of the wiring or parts that are connected to, or in the
(5) An unusually low dc collector voltage
vicinity of, high voltage. Also, discharge the capacitors
indicates a short circuit between the collector and
before touching the part.
ground, the collector and emitter, or the collector and
(3) Observe all proper precautions to
base or across the output impedance.
assure safety to personnel and equipment when making
4-4.
Troubleshooting Procedures.
high voltage and current measurements. Disconnect all
Troubleshoot the antenna using the chart below, and the
power and discharge capacitors before making any
tests in the Performance Standards, chapter 5 Perform
resistance measurements.
the tests in the order given in chapter 2 and
(4) Make sure that all cable and card
connections are correct before operating or testing
components.
4-1
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