Harman Kardon HK870 Owners Manual - Page 5

Protection, Circuit

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PROTECTION CIRCUIT STEREO POWER AMPLIFIER Do Not Open the Cabinet To prevent shock hazard, do not tamper with internal components for inspection or maintenance. Harman Kardon does not guarantee against performance degradation resulting from any modification. If water, a hairpin or wire accidentally enters the unit, immediately extract the plug from the AC outlet to prevent shock and consult an authorized Harman Kardon service station. If you use the unit under this condition, it may cause a fire or shock hazard. In Case of Moving the Unit Before moving the unit, be sure to pull out the power cord from the AC outlet and disconnect the interconnection cords with other units. Cleaning If the unit gets dirty, wipe it with a soft dry cloth. If necessary, wipe it with a soft cloth dampened with mild soapy water and then with a dry cloth. Never use benzine, thinner, alcohol or other volatile agent, and avoid spraying an insecticide near the unit. Protection Circuit When the power switch is turned on, the "wait" indicator illuminates for about 8 seconds. No sound will be heard during this time. This is the normal operation of the "turn-on muting protection circuit" which protects the speaker systems from turn-on transients. After about 8 seconds, the "wait" indicator will turn off and the amplifier wi ll operate. It is suggested that the preamplifier volume control be set to a low level during the turn-on period. It is also advisable to turn on al l other high fidelity components in the system before turning on the power amplifier. When a short circuit or a load of less than 2 ohms is placed across the speaker terminals for more than 4 milliseconds (4/1000 of a second), the protection circuit wil l activate and amplifier will be muted for about 8 seconds. The muting will turn off and the amplifier wil l begin operating again after 8 seconds. When the temperature of the internal heatsink rises too high, the protection circuit wil l activate and the amplifier will be muted. When the unit cools off, the amplifier will automatically become operational. However, unlike the turn-on and short circuit protection, the temperature protection may not restore operation in only 8 seconds because of the time required for the unit to cool off. 4

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PROTECTION
CIRCUIT
STEREO
POWER
AMPLIFIER
Do
Not
Open
the
Cabinet
To
prevent
shock
hazard,
do
not
tamper
with
internal
components
for
inspection
or
maintenance.
Harman
Kardon
does
not
guarantee
against
per-
formance
degradation
resulting
from
any
modification.
If
water,
a
hairpin
or
wire
accidentally
enters
the
unit,
immediately
extract
the
plug
from
the
AC
outlet
to
prevent
shock
and
consult
an
authorized
Harman
Kardon
service
station.
If
you
use
the
unit
under
this
condition,
it
may
cause
a
fire
or
shock
hazard.
In
Case
of
Moving
the
Unit
Before
moving
the
unit,
be
sure
to
pul
l
out
the
power
cord
from
the
AC
outlet
and
disconnect
the
interconnec-
tion
cords
with
other
units.
Cleaning
If
the
unit
gets
dirty,
wipe
it
with
a
soft
dry
cloth.
If
necessary,
wipe
it
with
a
soft
cloth
dampened
with
mild
soapy
water
and
then
with
a
dry
cloth.
Never
use
benzine,
thinner,
alcohol
or
other
volatile
agent,
and
avoid
spray-
ing
an
insecticide
near
the
unit.
Protection
Circuit
When
the
power
switch
is
turned
on,
the
"wait"
indicator
il
luminates
for
about
8
seconds.
No
sound
wil
l
be
heard
during
this
time.
This
is
the
normal
operation
of
the
"turn
-on
muting
protection
circuit"
which
protects
the
speaker
systems
from
turn
-on
transients.
After
about 8
seconds,
the
"wait"
indicator
will
turn
off
and
the
amplifier
wi
l
l
operate.
It
is
suggested
that
the
preamplifier
volume
control
be
set
to
a
low
level
during
the
turn
-on
period.
It
is
also
advisable
to
turn
on
al
l
other
high
fidel
ity
components
in
the
system
before
turning
on
the
power
ampl
ifier.
When
a
short
circuit
or
a
load
of
less
than
2
ohms
is
placed
across
the
speaker
terminals
for
more
than
4
milliseconds
(4/1000
of
a
second),
the
protection
circuit
wil
l
activate
and
amplifier
wi
ll
be
muted
for
about
8
seconds.
The
muting
wi
ll
turn
off
and
the
amplifier
wi
l l
begin
operating
again
after
8
seconds.
When
the
temperature
of
the
internal
heatsink
rises
too
high,
the
protec-
tion
circuit
wil
l
activate
and
the
amplifier
will
be
muted.
When
the
unit
cools
off,
the
amplifier
wi
ll
automatical
ly
become
operational.
However,
unlike
the
turn
-on
and
short
circuit
protection,
the
tempera-
ture
protection
may
not
restore
operation
in
only
8
seconds
because
of
the
time
required
for
the
unit
to
cool
off.
4