Operating instructions
CHAPTER
5
FIELD
MAINTENANCE
INSTRUCTIONS
Note.
This
chapter
cotttait'ts
infonnation
for
fielcl n.raintenance.
The
an-rount
by units
having
fìekl
tnaintenance
lesporlsibility
is
limitr.d
only
by
the tools
and
the
skill of
the lepailman.
of repair
that
can
ìre
lrelfor.nterl
test
ecluipment
avirilalrlt'
and
ì,1-
Section
l. TRoLTBLE
sHooTlNG
AT
FTELD
MATNTENANCE
LEVEL
69. Trouble-Shooting
Procedures
u.
Generul
The
first
step in
ser,vicing
a
cle-
Íective
radio
set
is
to sectionalize
the
fault.
Sectionalization
means
tracing
the fault
to the
inu.io)'
cotttltotr,ent
ot'
cít'ctLit
responsible
for
the
abnormal
operation
of the set.
The
second
step
is
to localize
the fault.
Localizatiolt
means
tlacing
the
fault
to the clefective
7rnr.f
respon-
sil.rle
for
the
abnormal
conclition.
Some
faults
-'rch
as burnecl-out
re-qistoLs,
t'-f
alcing,
and
sholtecl
transforntels
often
cau be
located
by
sight,
smell,
ancl
healiug.
The
majority
of
firnlts.
hrru'et'er',
must
be localized
by cltecking
t'oltcr
g
e u ttcl
t't,sístance.
b.
Component
Sectional,ization
ancl
Locali-
zuttott.
The
tests
listed
below
aid
in isolating
the
source
of trouble.
To
be
effective,
the
pro-
cedure shor"rld
be
follou,ed
in
the
order
given.
Remember
that
servicing
procedure
shoulcl
callse no
further
damage
to the
receiver
or
power
supply.
First, trouble
shoulcl
be localizcd
to a single
stage
or circuit.
Then,
the trorible
may
be isolatecl
u'ithin
that
stage or circuit
b1'
appropriate
voltage,
resistance,
and continuity
measLrrements.
The
service
procecllìre
is
sum-
marized
as follorvs
:
(1)
VíwaI ittspection.
The
purpose
of vis-
ual
ir-rspection
is
to locate
any
visible
trouble.
Through
this inspectiorr
alone, the repairman
frequently
mal'
discover
the trouble
or determine
the
stage in rvhich
the trouble
exists. This
inspection
is
valuable
in
avoiding
ad-
\co
313A
ditional
damage
rvhich
might
occur
to the
receiver
thror"rgh imploper
servicing
methods,
ancl
in
forestalling
futnre
failures.
(2)
Ittptr.t
resistance
ilteasut,e
nteril.q.
These
measltrements (pars.
73 ancl
7r1
)
pre-
vent
further
damage
to the
receir.'eL
from
possible
short
circuits.
Since
this
test
gives
an indication
of
the
condition
of
the filter
circuits,
its
func-
tion is
more
than
preventive.
(3)
OperationrLl
test.
The
operational
test
(pars.
75 and
76) is
importzrnt
oe-
cause
it frequently
indicates
the
gen-
eral
location
of trouble.
In
man)'
in-
stances,
the
information
gaineci
rvill
determine
the
exact
nature
of
the
fault.
To
utilize
this
information
fully,
all symptoms
mnst
be
inter-
preted
in
relation
to
one another.
(4)
Trouble-shootittg
cltat't.
The
trouble
s1'mptoms
listecl
in
these
charts
(parri.
77 ancl78)
ri'ill
aid
gleatlr.
in
localiz-
in.q
trouble.
(5)
Szgricl
sultstitirttr.tn.
The
principal
acl-
vantage
of
the signai
substitr,rtion
methocl
(pars.
80
thror"rgh
84) is
that
it
usualll-
enables
the repairman
to
locaiize
a tronble
accuratell'
ancl
quickll-
to
a
given
stage u'hen
the
genelal
location
of
the
trouble
is not
immecliately
evident
from
the
above
tests.
55