Werbung
MODEL HA-410 SERVICE MANUAL
MODELL HA-410 SERVICE ANLEITUNG
MODELE HA-410 SERVICE MANUAL
hs
Muting circuit
The muting circuit is employed to prevent click noise
generated in the tone and equalizer amplifiers during
switch operation (ON/OFF).
The signal between
the tone and main amplifiers is
turned on and off using a reed relay.
a) When the power is switched ON
When the power is turned ON, S1B which is inter-
locked with
the power
switch is simultaneously
closed.
When S1B is closed, —14V is applied to R814 and
the reed relay, then Q805 conducts after approx. 3
sec.,determined by the time constant of R814 and
C810, the reed relay then operates and the tone
circuit
and main
circuit are connected,
and clean
sound is produced.
b) When the power is switched OFF
When the power switch is turned off, current flowing
to the lead relay is shut off, the reed relay is
deactivated
and the tone circuit and main circuit
are disconnected.
Abnormal heat-generation detection circuit
(Protection of power circuit)
The circuit gives protection against abnormal temper-
ature rise.
A thermal lead switch is employed for
temperature detection. This uses the temperature (Cury
point) at which the magnetic material loses its magne-
tism because of the temperature rise, to operate the
lead switch (ON/OFF).
The magnetic material used in this circuit operates at
105°C anda
polyester film is used to install the radiator
and the lead switch to reduce the heat transmission by
2°C. This is for the purpose of giving an operational
output margin.
Operation of this circuit is shown in
Fig. 3.
Assume that the output is supplied to the load while
the reed relay is activated.
Heat which is generated in
the power transistor is dissipated by the radiation plate,
and when the temperature of the thermal lead switch,
which is installed together with the radiation plate, is
raised to 105°C, continuity is made and Q80S is cut off.
Accordingly, the reed relay is de-activated and the signal
does not enter the main amplifier, preventing temper-
ature rise.
When
the temperature
lowers, the thermal switch is
turned OFF, the reed relay is activated and sound is
generated.
When this condition is repeated, turn off
the power switch leaving it as it is for about 10 minutes
to lower the temperature of the radiator.
3. DC voltage detection circuit (Protection of speaker)
If DC voltage is applied to the speaker output terminal,
the speaker may be damaged.
Accordingly, when this
DC voltage appears, the speaker is protected by the fuse
at the DC power source.
The circuit is shown in Fig. 4.
(The structural com-
ponents are shown inside the dotted line.)
Assuming
that the trouble
occurs
in the L channel
causing generation
of (+) voltage, the (+) voltage is
taken to Q803 through R805 resulting in continuity,
breaking the gate of the thyristor CR808.
When the
thyristor
CR808
has continuity,
a large
current flows through the resistor R815, blowing fuse
F802.
When
a (—) current is generated, Q804 has
continuity, giving CR807 continuity and F801 is blown.
In both cases, fuses F801 and F802 are blown to give
more complete protection.
Tone
amplifier
" f t
Thermal lead switch
(operates at 105°C)
Fig. 4
Werbung
