Technics SU-Z400 - Muting and Relay Drive IC Description; Block Diagram Overview

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SU-Z400
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Mi DESCRIPTION OF MUTING/RELAY DRIVE IC (SVITA7317P) Mi BLOCK DIAGRAM
SPEAKERS
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TECHNICAL GUIDE
Protection circuit (I1C601 SVITA7317P)
|C601 serves as both protection and muting circuits.
@ Protection of power amplifier transistor against overload.
® DC protection of speakers from being damaged when the set is defective.
@ Muting operation until circuit operation is stabilized after power switch turned ON.
@ Muting operation to eliminate noise with power switch turned OFF. y [ Ste ue, - = :
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1. Protection of power amplifier against overload
(1) If excessive power is penetrated with a load less than the rating connected to speaker terminals or the speaker termi-
nals are short-circuited, a voltage a large current flow then Q621 turns on causeing the base voltage increasing of Q621.
(2) Q621 ON causes the hold circuit of Q602 and Q601 to turn ON, then the voltage at pin (2) of 1C601 decreases.
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Over load det
The
voltage
at
pin
(2)
is
usually
OV.)
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3
Be
tees
(3)
As
the
voltage
at
pin
(2)
of
1C601
decreases,
the
voltage
at
pin
(6)
rises
as
well,
and
the
output
relay
turns
OFF.
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NOTE: When the hold circuit is ON, the relay will not be reset even if the normal condition of the circuit is restored.
In that case, turn off the power supply and turn it on again.
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Rectifier
2. DC protection
(1)
If
DC
is
generated
at
the
speaker
terminal
due
to
defective
circuit,
then
DC
will
be
applied
to
1C601
pin
(2).
(2) The DC detection circuit of |C601 functions and the voltage at pin (6) rises, then the output relay turns OFF.
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3. Muting circuit with power ON
(1) With power turns ON, positive (+) voltage supply to C604 through R615 and R614.
(2) When the voltage across C604 (i.e. voltage at 1C601 pin (8)) gradually rises up to about 1.3 V, the voltage at pin
(6) drops and then the output relay turns ON. .
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VOLTAGE AMP
NOTE: The time required for voltage rise at pin (8) depends upon the time constant of R614 and C604. . (a)
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4, Muting circuit with power OF F > 5
, 2
(1) Voltages from power supply circuit (C904, R612) of large time constant and from power supply circuit (C602, Q 2
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R610) of small time constant are applied to pin (1) of 1C601, which is usually about —O.5V. = Ss
(2)
When
power
turns
OFF,
the
negative
(—)
voltage
of
small
time
constant
lowers,
but
the
positive
(+)
voltage
of
Bs
large time constant will not immediately drop. Accordingly, the voltage at 1C601 pin (1) rises.
(3) As the voltage at pin (1) rises, the voltage at pin (6) rises as well, causing the output relay to turn OFF. %
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“Relay is immediately turned OFF with power OFF, therefore there is no circuit noise trouble due to voltage drop. as
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