NAD 300 Service Manual page 12

MAIN AMP
&
DOLBY NR ALIGNMENT
NOTE:
1
.
The
proper bias adjustment
is
most important to
assu
re
correct performance of the amplifier.
'
Bias
adjustment is
necessary
if
any
of
the
transistors are replaced in
the power amplifier
circuitry
or
the
amplifier exhibits
overheating
of
the output
transistors under
normal
operating conditions.
2.
This
Receiver has
built-in
overload thermal protections, one
is installed
within power
trans-
fornier
and
the others are installed on heat sinks of power transistors.
ln
case
of the thermal protector of
power transformer, when the temperature of
thermal
protector
reach
to
135t5'C, the thermal protector
will
be automatically cut out,
and
as
soon as
the
temperature goes down
to
110t10'C, the thermal protector turns back
on
automatically.
The protectors of
heat sinks
have
the
same
effect
as
above
except
for
working temperature.
When
their temperature
rises
up
to
115t5"C,
these protectors
will
be automatically cut
out,
and
as
soon as
the temperature falls down
to 40t19'9,
these
protectors turn
back on
automatically.
STEP
ADJUSTMENT INDICATOR REMARKS
1
VR601a,
b
(Bias control)
DC
Voltmeter
Adjust
for
0.025V
across
R629a, b
or
R630a,
b
(0.82) with
no signal.
2
VR602a, b (DC
balance
control
of
output)
DC
Voltmeter Connect DC Voltmeter to SPEAKE
R
terminals.
Adjust
for 0Vt20 mV
reading
on
DC Volt-
meter.
3
vR702
(output
level con-
trol of
400
Hz
TONE)
AC Voltmeter
Connect
AC Voltmeter to output terminal
(Pin #11 of 7110 DOLBY NR Board.
Adjust for 30 mV
reading
on AC Voltmeter.
4 VR701a,
b
(DOLBY
level
cal.
of SIGNAL
Meter
SIGNAL
Meter
Adjust for DOLBY
level on
SIGNAL Meter
reading
with
400
Hz
TONE button (located on
the Front
Panel)
pushed
in position, with
DOLBY NR switch to the PLAY position.
12