Crown D-150 - D150 Parts List; Circuit Board Components; Chassis Components

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me
SYMPTOM PROBABLE CAUSE AND REMEDY
High noise level Bad solder joints. Visually inspect
the defective channel components
and leads.
Poor ground conmections. Check
all ground wires. Check output
jack ground. Check insulating
washers on input jacks.
Use a. wattmeter and check the power consumption at the ampli-
fier output when the amplifier is turned on (idling) but carrying no
signal. The amplifier must draw less thar 30 watts with the ac line
voltage at 120 volts. A typical reading is 20 watts.
Bias diode (D2 through DS)
open. Replace.
Shorted positive output or driver
Stage along witha shorted rieg-
ative output or driver stage.
+45 shorted to chassis at
€2i or Q10.
Output may be shorted at C22 or
Q12 collector.
SYMPTOM
High quiescent ac
power input
5.8 BIAS. LEVEL CHECK.AND ADJUSTMENT
Refer to Figure 5-5. The correct bias level for the D-150 amplifier is
set at the factory and will not usually require adjustment uniess
components affecting the level are replaced: Component changes
likely toalfect bias settings are the pre-driver, driver, outputstages
and bias diodes (02-05).
Correct bias maintains the driver and pre-driver stages atnormal
operating levels and-keeps the output stages turned off. This con-
dition is achieved whien a voltage of 325 + 15: mv (.310-.340-voits)
appears across the output stage bias resistor (R11) for each
charmel.
a. To check bias levek
1. Remove board and. electronics cover from the aniplifier
(paragraph 5.4.1, Step.4).
2,
Remove
bottom
cover
from
the
amplifier
(paragraph
5.4.1,
Step.2).
3.
This-check
is
to
be
made
with
the
amplifier
idling
(no
input
and
ne
toad).
4..
Connect
power
to
amplifier
and
allow
unit
to
warm
up
to
normal
operating
temperature.
27
CAUTION 1!
Do
not
measure
bias
level
voltage
until
unit
is
fully
warmed
up.
Voltage
begins
to
climb
at
turn-on,
peaks
_
and
gradually
drops
to
the
normal
level.
Measure-
ments
taken
during
warm-up
are
likely
to
be
mis-
leading.
5.
Measure
the
voltage
across
one
of
the
output
stage
bias
re-
sistors
for
each
channal{R120,
R127;R220;
R227).
Voltage
should
be
between
310-340
mv.
If
voltage
is
abnormal,
use
the
following
procedure
te
obtain
correct
bias
level
vottage.
b. To adjust bias level voltage:
Adjustrnent
of
bias
level
voltage
is
made
by
changing
the
value
of
the
selected
resistor
in
the
bias
circuit
(R141).
These
re-
sistors
are
mounted
in
plug-in
sackats
on
the
Main
PC
Board.
Generally,
selected
bias
resistors
range
trom
33
té
several
hundred
ohms.
Carbon
resistors,
10%
tolerance,
are
normally
used,
1.
H
the
measured
bias
voltage
was
high,
replace
the
factory-
installed
resistor
with
one.of
higher
value.
This
willlowerthe
bias
voltage:
2.
If
the
measured
bias
voltage
was
tow,
replace
the
factory-
installed
resistor
with
one
of
lower
value.
This
will
raise
the
bids
voltage.
Continue
replacing
the
selected
resistor,
using
the
above
procedure,
to
bring
the
bias
voltage
as.
close
to
325
mv
as
possible:
WAIN FE BORK {Gomgaoant Side)
F “l
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te
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FIGURE 5-5, BIAS LEVEL CHECK COMPONENTS
AURA BREEN