TM 11-6625-298-14
CHAPTER 6
GENERAL SUPPORT MAINTENANCE INSTRUCTIONS
Section l. TOOLS AND EQUIPMENT
6-1. General
the tools and test equipment available and by the
skill of the technician.
This chapter contains instructions for general
support of Ohmmeter ZM-21*) /U. The types of
6-2. Tools and Equipment
repair that can be performed by units having
For a listing of tools and test equipment needed
general support responsibilities is limited only by
for general support maintenance, see appendix C.
Section Il. TROUBLESHOOTING
frequently indicate the general location of trouble.
In many instances, the tests will help in deter-
a. General. The first step in servicing a
mining the exact nature of the fault.
defective ohmmeter is to sectionalize the fault.
(3) Troubleshooting
table. Troubleshooting
Sectionalization means tracing the fault to one of
the major circuits responsible for the abnormal
gives (or references) corrective measures. Such a
operation. The second step is to localize the fault.
table obviously cannot include all trouble symp-
Localization means tracing the fault to a particular
toms that may occur. The technician should use
stage or network within one of the major circuits.
this chart as a guide in analyzing symptoms that
The third step is to isolate the fault. Isolation
may not be listed.
means tracing the fault to the defective part
(4) Intermittent troubles. In all the tests, the
responsible for the abnormal condition. Some
possibility of intermittent troubles should not be
faults, such as burned-out resistors, arcing, and
overlooked. If present, this type of trouble often
shorted transformers often can be located by sight,
may be made to appear by tapping or jarring the
smell, and hearing. The majority of faults,
equipment. It is possible that some external
however, must be isolated by checking voltages
connections may cause trouble. Test wiring for
and resistances.
loose connections; move wires and components
b. Component Sectionalization, Localization,
with an insulated tool, such as a pencil or fiber
and Isolation. Listed below is a group of tests
rod. This may show where a faulty connection or
arranged to simplify and to reduce unnecessary
component is located.
work and to aid in tracing a trouble to a specific
c. Ohmmeter. A knowledge of the functioning of
component. Follow the procedure in the sequence
the ohmmeter is necessary for the technician. See
given. A technician must be careful not to cause
paragraphs 5-1 through 5-7 for pertinent in-
further damage to the ohmmeter while it is being
formation. To supplement the troubleshooting
serviced.
table and to locate parts, refer to the following
(1) Visual inspection. The purpose of visual
illustrations:
inspection is to locate faults without testing or
(1) Schematic diagram (fig. 5-5).
measuring circuits. All visual signs should be
(2) Functional diagram (fig. 5-6).
observed and an attempt made to sectionalize the
(3) Illustrations showing location of parts (fig.
fault to a particular function.
5-1, 5-5, 6-1, and 6-2).
(2) Operational tests. Operational tests
