Phase Linear 400 Service Information

BIAS
The
bias
control
is
present
at
the
factory
and
should
not
be
adjusted
or
rotated
needlessly.
Adjustment
is
only
re-
quired
if
it
is
rotated
accidentally
or
if
bias
transistor
Q3
is
replaced.
Step
#1.
Locate
test
point
TP;
on
the
circuit
board.
Connect
a
voltmeter
positive
lead
to
TP;
(negative
end
of
Ce)
and
the
negative
lead
to
the
hot
(red
or
white)
speaker
output
terminal.
Step
#2.
Allow
at
least
5
minutes
warmup:
This
is
extremelu
important
and
cannot
be
overemphasized.
Remove
all
input
and
output
connections
(no
load),
and
have
level
controls
fullu
counterclockwise.
Adjust
bias
control
to
read
0.35
volts.
This
completes
alignment.
SECTION Ill
TROUBLESHOOTING
Sumptom:
Blows
output
fuses.
If
the
output
fuses
blow
immediatelu
and
repeatedlu,
one
or
more
output
transistors
mau
have
shorted.
Generallu,
when
one
output
transistor
fails,
it
causes
at
least
one
other
to
fail.
If
a
determination
has
been
made
that
one
or
more
output
transistors
has
shorted,
the
following
method
is
re-
commended
to
specificallu
locate
the
defective
unit/units
among
the
group
of
eight
апа
to
get
the
amplifier
back
into
operation.
Step
#1.
Set
up
the
amplifier
on
the
test
bench
as
shown
in
figure
#1.
The
heat
sink
closest
to
the
power
trans-
former
holds
the
left
channel
output
transistors.
Use
a
V.T.V.M.
(RCA
Volt-Ohmyst
or
equivalent)
on
the
resistance
Rxl
range.
Connect
the
negative
lead
to
the
collector
bus
wire
of
the
sus-
pected
bank
of
output
devices.
Starting
with
the
top
transistor,
measure
the
resistance
at
its
emitter
with
the
positive
lead.
If
that
transistor,
or
any
in
that
bank
of
transistors
is
shorted,
the
meter
will
indicate
a
fraction
of
an
ohm.
If
the
transistors
are
good,
the
meter
will
indicate
a
high
resistance
circuit.
If
the
meter
indicates
a
fraction
of
an
ohm,
note
the
resistance
and
proceed
from
emitter
to
emitter,
testing
in
turn
each
device.
The
meter
will
indicate
a
fraction
of
an
ohm
on
each
emitter
be-
cause
the
transistors
are
connected
in
parallel
through
their
emitter
transistors.
However,
when
the
defective
one
is
tested,
4

Phase Linear 400 Specifications

General

Brand	Phase Linear
Model	400
Category	Amplifier
Language	English