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4-4
MAINTENANCE
Orban Model
464A
2)
Record
all
control
and
internal
jumper
settings.
3)
Check power
supplies.
a)
Set the
power
button
to
OFF.
b) Verify the
following
resistances:
Between:
And:
Resistance:
Power
cord
ground
pin
Chassis
On
Each
of
the
power
cord blades
Chassis
°°n
One
power
cord blade
The
other
blade
°°n
c)
Set
the
power
button
to
ON.
d) Verify
that
the resistance
between
the
two power
cord blades
is
about
100n
(for
a
110V
unit).
For
a
220V
unit,
the resistance
should
be
about 350n.
e)
Remove
the
jumper
connecting
the
GROUND
^
and
^
terminals
on
the rear
panel.
f)
Verify the following
resistances:
Between:
And:
Resistance:
GROUND
^
GROUND
^
00 12
GROUND
^
Chassis
on
GROUND
^
Test point
TP19
(power supply
common)
on
g)
Replace
the
jumper
connecting
the
ground
^
and
^
terminals.
h)
Power
the
unit
i)
Verify
that
the negative unregulated
power
rail is
between
-18V
and
-26
V,
and
that the positive
unregulated
power
rail
is
between
+18V
and
+26V.
j)
Verify
that
the outputs
of
the
±15V
regulators
at test
points
TP18
(+)
and
TP20
(-) are
15.00V ±0.75V.
k) Verify
with an
oscilloscope
that
the noise
and
ripple
on
the regulated
power
supply
rails is
below
4mV
peak.
l)
Place
jumper
A
in the
"DEFEAT"
position.
m)
With
a
digital
voltmeter, verify
that
the
voltage
at test
point
TP2
is
-14.00V
±0.75V.
n) Verify
that
the voltage
at
test
point
TP3
is
+
14.00V ±0.75V.
o)
Place
jumper
A
in the
"OPERATE"
position.
p)
Adjust
CLIPPER BIAS trimmer
R2
to
produce
-5.5V ±0.1V
at
TP2.
q) Verify that the voltage
at
TP3
is
+5.5V
±0.1V.
r)
Place
jumper
A
in the
"DEFEAT"
position.
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