Marantz 2240 - Power Supply Unit; Speaker Protector Relay Circuit

operating
as
a
power
transistor
protection
circuit.
Excessive
current
flow
in
the
power
output
stage
is
detected
by
the
resistors
R725
and
R726
and
the
resultant
variation
is
applied
to
the
transistors
H710
and
H711
and
make
them
turned
on.
This
decreases
the
base
biasing
current
for
H714
and
H715.
In
this
way
the
current
flow
in
the
power
output
stage
(HOO1
and
HO02)
is
restricted
within
a
safe
predetermined
value.
6.
POWER
SUPPLY
UNIT
The
power
supply
unit
consisting
of
transistors
H801,
H802
and
H803,
which
operates
as
an
automatic
voltage
regulator
provides
+35V
DC
to
all
of
the
audio
amplifiers
except
power
amplifiers,
and
H804
which
operates
as
the
voltage
regulator
provides
+14V
DC
to
the
tuner
section,
and
H805,
H806
and
H807
which
operates
as
the
speaker
protector
to
relay
circuit.
7.
SPEAKER
PROTECTOR
RELAY
CIRCUIT
The
speaker
protection
circuit
consisting
of
H808,
H809,
H810,
etc
protects
the
speaker
systems
against
any
loud
‘‘pop’’
sound
developed.
This
circuit
is
so
designed
that
no
sound
is
heard
for
the
first
three
or
five
seconds
after
the
power
switch
is
turned
on
by
the
time
constant
circuit
consisting
of
C809
and
R813.
This
circuit
also
protects
the
speaker
systems
against
some
troubles
due
to
DC
off
balance
between
the
speaker
system
terminals
by
instantly
operating
the
relay
and
cut
off
the
speaker
systems
from
the
circuit.
When
DC
off
balance
voltage
(positive)
is
developed
between
speaker
terminals
by
possible
defects
such
as
broken
power
transistor,
short-circuits,
or
broken
potentio
meter
R707,
as
the
base
of
H805
is
connected
to
the
speaker
terminal,
the
transistor
H805
is
turned
on
by
this
offset
voltage
developed
and
this
makes
the
transistor
H806
and
H807
turns
off,
thus
cutting
off
the
relay
and
disconnecting
the
speaker
from
the
output
circuit.
When
negative
offset
voltage
is
developed,
this
voltage
directly
turns
off
the
H806
and
H807,
thus
speaker
is
cut
off
from
the
circuit
and
protected.
The
circuit
also
protects
the
speaker
systems
from
the
possible
damage
when
the
amplifier
is
over-driven
by
very
low
frequencies
such
as
7
or
lower
cycles.
:
REMOVE SCREW
REMOVE THIS COVER
Figure
2.
Remove
the
Terminal
Cover