TM 11-5840-281-35/1
tors C-6988/TPN-18 may be used as an aid in isolating a
functional section, or in some instances, down to a
trouble from a system level to a functional circuit level. It
replaceable unit, assembly, or circuit card.
is important to consider that a not-so-apparent trouble
can result in other more obvious troubles. For example,
3-8.
Isolating Trouble Within a Functional Section
a broken wire on a switch can prevent the operation of a
to a Replaceable Unit, Assembly, or Circuit
relay, and the inability of the relay to operate can prevent
Card
the application of power to an antenna drive motor which
results in the obvious symptom of failure of the antenna
The order in which testpoints are selected within a
to rotate. Sometimes an accurate running log on
functional section to isolate a trouble down to a
equipment symptoms can result in the disclosure of
replaceable unit, assembly, or circuit card, should be
intermittent or hard-to-find minor troubles that elude
determined by which choice appears to be the most valid
normal procedures.
and requires the least amount of time and test
equipment. Use the functional schematics (fig. 7-5
3-5.
Symptom Elaboration
through 7-16), the waveform charts (fig. 3-1 through 3-
After an equipment trouble has been recognized,
identification of the faulty unit, assembly, or circuit card.
operation of the equipment should be used whenever
To assist in locating and identifying components and
possible to further elaborate the extent of the trouble
parts of Radar Set AN/TPN-18, see parts location
symptom.
Checking or manipulating the operating
controls sometimes may eliminate an apparent trouble.
of this chapter.
3-6.
Listing of Probable Faulty Functions
3-9.
Isolating Trouble to a Replaceable Part
Mentally or literally list the functional sections which
After the trouble is isolated down to a unit, assembly, or
could result in the available trouble symptoms. The
circuit card, the next step is to determine if the faulty unit
choices of possible faulty functional sections are based
or assembly is reparable by replacement of a part.
on knowledge of normal equipment operation,
information contained in this manual, and identification of
faulty unit or assembly is reparable, use the waveform
trouble symptoms. Refer to the block diagram and
functional schematic diagrams in chapter 2 of this
schematic diagrams with applicable test equipment to
manual for assistance in listing probable faulty functions.
check for faulty operation, and to isolate the trouble to a
Descriptions of the functional sections and circuits are
replaceable part. For components that are inaccessable
also contained in chapter 2.
while installed in the equipment, use extender cards
supplied with the equipment or patch cables (fig. 7-107).
3-7.
Isolating Trouble to a Functional Section
After a unit or assembly has been repaired or replaced,
test the unit or assembly in accordance with paragraph
4-1 to
determine if
the repair has been performed
If a trouble in more than one functional section could
satisfactorily. Refer to chapter 2 for descriptions of the
result in the same symptoms, a minimum number of
applicable circuits.
testpoints, either at or near the outputs of the functional
sections, should isolate the trouble down to one
3-10. Radar Set Group Direct Support Troubleshooting Chart
a. Loose mounting bolts in
a. Check mounting bolts on
not rotate on level plane as
azimuth Antenna Drive TG-
azimuth Antenna Drive TG-
indicated on clinometer when
113/TPN-8 and antenna
bubble level on elevation
tube.
support tube for tightness.
Antenna Drive TG-114/TPN-8
indicates level.
b. Bubble level on elevation
b. Refer to higher category
Antenna Drive TG-114/TPN-8
maintenance.
3-2