Realistic STA-21 - Page 11

TP
14
161514131211109
rc
101
LA
3350
1
23
4
5 6 7 A
FM
STEREO
ALIGNMENT
SET-UP
FM ANT
TERMINAL
TAPE
OUT
JACK
Figure
8
Figure
9
BRIEF DESCRIPTION
OF PROTECTIVE
CIRCUIT
lf speaker
terminals
are
shorted,
or Load impedance
of one
channel
(Left
or
Right)
comes less
than 4
ohms,
excessively high
current flows
from Emitter
to
Collector
of TR
313
(or
TR
314) and
a high voltage appears
across R
323
(or
R3241.
This
high voltage
goes
to
Gate of
SCR D315
after being rectified
by D
308
(or
D
309). When
the
voltage
between
Cathode
and
Gate increases
to about
0.7 V,
SCR D315
will be
turned
on.
Voltageat
Pin
No. 15on
PowerSupply
Board
goesto
-1
V
to
0V,
PRE
AMP
and TONE
circuits
will
stop
functioning
and
thus
protect
MAIN
Amp.
lf
this should
occur,
the amplifier will
automatically
shut down
and
output will
drop to zero. Turn
the
receiver
off to
reset
the
protective
circuit.
When the
problem
is
corrected,
turn the receiver
on again.
TR
3II
(TR
3t2)
R
321
(
R
322)
R
333
R
332
C
3t9
POWER
SUPPLY
CIRCUIT
PRE
&
TONE
B+
D3o8
;
a
(D3oe)
I i
tI
OUT
PUT
Lor R
MAIN
AMP CIRCUIT
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