5.
Repairs
5.1
Reouired
Measuring
Eguigment
See
section
3.2.1.
§.2
Trouble-shooting
Prior
to
electrical
testing,
the
boards
and
the
components
should
be
checked
for
Visible
defects.
Then
trace
the
faults
through
the
following
stages
(see
signal
level
diagram):
—
power
supply
-
AF
generator,
input
amplifier,
L/R
indication
—
generation
and
processing
of
pilot
tone
—
coder
circuitry,
output
amplifier
—
SCA
modulator
(see
separate
manual)
5.2.1
Power
Suquy
Check
the
supply
voltages
+12
V
at
K70.6/7,
-12
V
at
K70.l/2
and
+21
V
(unstabilized)
at
K70.8.
5.2.2
AF
Generator,
Input
Am
lifier,
L
R
and
L
+
R
Indication
Set
the
input
selector
8101
to
position
R
=
L
and
check
the
level
with
the
indication
selector
8106
in
positions
R/L
and
R
+
L.
The
indication
must
be
+6
dEm
in
both
channels.
In
case
of
an
error,
carry
out
further
checks
according
to
the
level
diagram
in
Fig.
5
(test
points
MPlOl
to
108,
MPlll,
links
BRlOl
to
103).
5.2.}
Generation
and
Processigg
of
Pilot
Tone
Set
the
indication
selector
to
PILOT
and
check
for
the
correct
pilot
level
on
the
lower
scale.
The
nominal
level
is
indicated
with
the
pilot
mode
selector
(5107)
set
to
”on”
and
”A
AU";
there
is
no
indication
when
the
pilot
mode
selector
is
in
position
”off".
If
there
is
a
problem,
check
with
an
oscilloscope
according
to
Fig.
6
(test
points
MP114,
MPllS
and
specified
pins
of
the
ICs).
Check
the
frequency
with
a
counter
(test
point
MP114
or
Sthl.3b).
R
38122
—
23
NJ