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4-10
MAINTENANCE
Orban Model
464A
e)
Turn
the
L INPUT
atten
control
fully
clockwise,
and
set
the
L
HF
LIMIT button
to
OPERATE.
f)
Place
jumper
B
in the
"FLAT"
position.
g)
Disconnect
the
audio
oscillator
from
the
Co-Operator.
h)
Connect
the tracking generator
output
of
the
spectrum
analyzer
to
the
LEFT
IN
HI terminal (ground
the
LEFT
IN
LO
terminal).
Set the
spectrum
analyzer
for
a
20-20,
000Hz
log
sweep
and
a
2dB/division
display.
Adjust
the generator's
output
level
until
the
HF
LIMIT
indicator
does not
light.
i)
Connect
the
spectrum
analyzer's input
to
TP8.
j)
Verify a
flat
response (±0.25dB)
for
each
position
of
the
L PRE-EMPHASIS
switch.
k) Set the
L PRE-EMPHASIS
switch
to 25ns.
l)
Slowly
increase the tracking generator's
output
level until limiting action
is
clearly
visible.
m)
Verify
that the
limiting action
is
as
shown
in Fig.
4-1 for
each
position
of
the
L
PRE-EMPHASIS
switch.
n)
Check
the
right
channel high-frequency
limiter
by
repeating
the
above
(both
parts
1
and
2) for the right
channel.
Use
the
right
channel
controls, terminals,
LED,
trimmers,
and meter
instead
of
the
left,
and
substitute
TP9
for
TP8,
TP10
for
TP7, and jumper
C
for
jumper
B.
o)
Disconnect
the
spectrum
analyzer
from
the
Co-Operator.
Fig.
4-1: Limiting
Curves
(see step
9m)
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