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Co-Operator
MAINTENANCE
s)
Adjust +3
volt
trimmer
R8
to
produce
+3V
±0.1V
at test
point
TPM.
t)
Verify
that
the voltage
at
pin
8
of
IC5
is
-0.70V
±0.15V.
4)
Check
the
input stages.
a)
Connect an
audio
oscillator to
the
left
in hi terminal.
Set
the
oscillator's
frequency
to
1kHz
and
its
output
level
to
-lOdBu.
OdBu
=
0.775V
RMS.
The dBm/600n
scale
commonly
found
on
test
instruments
can be
read
as
dBu
for
this
application.
b)
Ground
the
LEFT
IN
LO
terminal.
c)
Connect
an audio voltmeter and an
oscilloscope
to
E28.
d)
Turn
the
L INPUT ATTEN
control
fully
clockwise.
e)
Verify a
level
of
-16.5dBu ±0.5dB
at
E28.
f)
Verify
that
the signal
at
E28
is
a
sine
wave
of normal
appearance.
g)
Mute
the
oscillator,
verify that there
is
no "popcorn"
noise or
oscillation,
then
restore the
signal.
h)
Rotate
the
L INPUT ATTEN
control
through
its
range. Verify
smooth
and
quiet
operation
of
the
control.
i)
Turn
the
L INPUT ATTEN
control
fully
clockwise.
j)
Remove
the
ground from
the
LEFT
IN
LO
terminal.
k)
Connect
the
audio
oscillator to
both
the
LEFT
IN HI
and LEFT
IN
LO
terminals.
l)
Verify a
common mode
cancellation
of
at least
40dB.
m)
Check
the
right
channel
input stage
by
repeating the
above
for the right
channel.
Substitute the right
channel
controls
and
terminals,
and
E32
for
E28.
n)
Disconnect
the
oscillator,
voltmeter,
and
oscilloscope
from
the
Co-Operator.
5)
Check
VCA
stages.
a)
Connect
the
audio
oscillator to the
LEFT
IN Hi terminal,
and ground
the
left
IN
LO
terminal.
Set the
oscillator's
frequency
to
1kHz
and
its
output
level to
-lOdBu.
b)
Connect
a
THD
analyzer,
audio
voltmeter,
and
oscilloscope
to
test
point
TP7.
c)
Set
the
L LEVEL
and L
COMPR
buttons
to
OFF.
Verify
that
the
L
INPUT
ATTEN
control
is
turned
fully
clockwise.
d)
Center
L GAIN
trimmer
R129
and
L
THUMP NULL
trimmer
R1
19.
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