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HITACHI
HA-3800
CHECKING THE OPERATION OF THE PROTECTION CIRCUIT
When
the output circuit is repaired by replacing
the
power transistors, etc.,
perform
and
operation
check
on
the
ASO (Area
of
Safe
Operation)
detection
circuit.
Operation check
of the
ASO detection
circuit for
the output transistors
Connect
the audio oscillator
to
the TUNER
IN
ter-
minals
with the
speaker
terminals
unloaded
(speaker:
disconnect).
Set
the frequency
of
the
audio oscillator
at
I
kHz
and
adjust
the level
of
the
input
signal
so
that the
voltage
at the
speaker
terminals is
approx.
5V rms.
Under
these
conditions, short-circuit
the
speaker ter-
minals
of
the
channel
to
which thb
input
signal
is
ap-
plied
using
a
lead
wire,
etc.
If
this short-circuit
makes
the ASO detection
circuit
operate, no
output
appears at
the
speaker
terminals
even
if
the lead wire used for
short-circuiting
is
removed.
Next,
turn
off
the
power
switch
and,
after approx. l0
sec.,
turn
the power switch on again. When output
comes
out of the
speaker
terminals, this
indicates
that
the
ASO
detection
circuit
is operating
normally.
Fig.
5
\2
v
o Phenomena
and
remedies
when the protection circuit
operates
Protection
circuit
operates
Set the
power switch
to
OFF
and Volume
Control
MlN.
Turn the
power
switch
ON
After
6-10
seconds,
play
a
record
or
receive
a
broadcast,
and gradually
raise
volume.
the
speaker sound
disappear?
Volume
Control MIN
and
the
power
switch
to
OFF.
re
the speaker cords shorted
ls
the
speaker
impedance correct?
Amp.
is normal. When the unit
operates
without the
speaker
cord shorted,
the
ASO
detec-
tion circuit
is
operation.
Use
the unit with
Volume Control
a
little
power.
Use
speakers
with
impedance
of
8
-
16
ohms
when using
2
sets
of
loudspeaker
systems
simultaneously.
6
v
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