
Check
the
4
MHz
REF
Signal
1.
Connect
a
cable
from
the
RF
OUT
to
input
R.
2.
Press
4
PRESET
5.
3.
Use
an
oscilloscop
e
to
observ
e
the
4
MHz
reference
signal
at
A10P2-6.
If
the
signal
do es
not
resem
ble
Figure
8-3,
troublesho
ot
the
signal
source
(A12P2-36)
and
path.
If
the
signal
is
go
o d,
the
probability
is
greater
than
90%
that
the
A10
assem
bly
is
faulty
.
F
or
conrmation,
p erform
\Chec
k
A10
b
y
Substitution
or
Signal
Examination."
Figure
W
A
VE8
here.
Figure
8-3.
4
MHz
REF
W
a
v
eform
Check
A10
b
y
Substitution
or
Signal
Examination
If
the
4
MHz
REF
signal
is
go
o d
at
the
A10
digital
IF
assem
bly
,
c
hec
k
the
A10
assem
bly
b
y
one
of
the
follo wing
metho ds:
Substitute
another
A10
assem
bly
or
Chec
k
the
signal/con trol
lines
requiredfor
its
op eration.
The
pins
and
signal
sources
of
those
lines
are
iden
tiedin
T
able
8-1 .
It
is
p ossible
that
the
A9
assem
bly
may
not
b e
pro
viding
the
necessary
signals.
These
signal
c
hec
ks
allo w
y
ou
to
determine
whic
h
assem
bly
is
faulty
.
Some
of
the
w
a
v
eforms
are
illustratedb
y
Figure
8-4
andFigure
8-5.
If
the
substitute
assem
bly
sho
ws
no
improv
emen
t
or
if
all
of
the
input
signals
are
v
alid,
con
tinue
with
\Chec
k
the
4
kHz
Signal."
Otherwise
troublesho
ot
the
susp ect
signal(s)
or
consider
the
A10
assem
bly
faulty
.
DRAFT
3/21/106
15:13
Receiv
er
Troubleshooting
8-5
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