TM 11-5840-281-35/1
Etched circuit cards, i-f amplifiers, and mechanical
d. Types of trouble that would satisfy all of the
assemblies of Radar Set AN/TPN-18 are to be referred
above conditions are: open bypass or coupling
to a higher category of maintenance for repair. At direct
capacitors, capacitors that have changed value, and an
support maintenance, these components are to be
interstage transformer with shorted turns.
replaced by identical serviceable components. Refer to
e, When an open capacitor is suspected,
the maintenance allocation chart (MAC), Appendix C in
connect a known good capacitor of equal value across
TM 11-840-281-12 for the allocation of maintenance
the capacitor and check the operation of the component.
responsibilities, tools, and test equipment. Refer to TM
f. When all other possibilities of trouble are ruled
11-5840-2814-35P for applicable repair parts lists.
out, substitute a good part for the one suspected of being
defective.
g. A type of defective component that may not
3-48. Repair of Electronic Parts
be uncovered by the above procedures may be a
capacitor that has changed value.
a.
Electronic parts generally are not
economically reparable, and must be replaced with new
parts requisitioned from stock. With few exceptions, a
3-49. Extent of Disassembly
replacement part must be an exact duplicate of the
original part.
When an exact replacement is not
a. Disassembly of units and components should
available, a part with similar electrical characteristics,
be extended only to the point required to effectively
and equal or better reserve capabilities, may be
repair or remove and replace specific defective parts.
substituted. Never use a substitute part with a working
Consideration should be given to the possibility of
voltage or power rating lower than that of the original
making repairs without actually removing the defective
part. Avoid substituting parts with different physical size
part. Unnecessary disassembly or removal of electronic
or shape in high-frequency circuits because of the
parts increases the danger of upsetting circuit responses
possible trouble resulting from stray capacitance.
and producing compound troubles.
b. In general, all sealed components must be
b. A replacement part should always occupy the
replaced if defective. This includes capacitors, resistors,
same position as the original part. In cases where there
crystals, tubes, potted transformers and chokes, and
is a possibility of improper reassembly or installation of
sealed relays and switches. Open type transformers,
parts, a parts tray or a table receptacle should be
chokes, and coils are reparable only when the fault is
provided so that the parts can be placed, as removed, in
near the terminal. Unsealed relays and switches may be
approximately their proper positions in relation to each
repaired when faulty operation is due to corroded or dirty
other and to the complete unit. Keep the parts in this
contacts, or to mildly pitted or burned contacts.
order until final assembly is complete. Disassembly
c.
Do not subsitute parts indiscriminately.
should be made with the point in mind that another man
Substitute parts that must be soldered in place only when
may be required to do the reassembly. Accordingly, a
all of the following conditions are satisfied:
suitable diagram or tag should be made before
(1) The trouble has been localized to a
disassembly, showing orientation and connections of the
specific stage.
various parts wherever these are not obvious. Note
(2) Suspected pluck-out components have
polarity markings of paper and electrolytic capacitors.
been replaced.
Use scribed reference marks where suitable. Do not
(3) All voltages and measurements and
mark bearing surfaces or threads. When in doubt as to
other in-circuit resistance measurements have been
the exact position or connection of a part, refer to the
made.
illustrations or diagrams of the unit.
Section V. REMOVAL AND REPLACEMENT; DISASSEMBLY AND REASSSEMBLY
for mechanical and electronic assemblies of Radar Set
3-50. General
AN/TPN-18 within the scope of direct support
maintenance.
For
location
of
parts,
This section provides direct support maintenance
removal and replacement, disassembly, and reassembly
3-55
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