Sharp OPTONICA SM-1616H - Circuit Description - Equalizer and Output; Equalizer Circuit Design; IC Output Circuit Handling

mEQUALIZER CIRCUIT (See Figure 9)
The equalizer circuit is powered by the two-power-supply
(+19.7V, —19.7V) system.
Q201 and Q202 in the first stage are high-amplification and
low-noise type FET and input signals to these transistors
are directly coupled with the second stage.
Q203 and Q204 in the second stage are low-noise transistor,
in which almost all of the gains for the equalizer circuit are
assured. The third stage is composed of Q205 and Q206 and
R212 82k
R26 R222
C2i2
.0056G (ML)
14 c2i8
K lO/I6V
R2
6.
; A | 33
+
+ Sr22l0 220 SEK
4.7|K 3.3/50V ;
! H
2
16G
it includes DC load resistor R213 and R214: the resistance of
this
resistor
is
limited
to
the
minimum
to
assure
signal
inputs
in
a
higher
frequency
range.
C217
and
C218
are
boot
strap
capacitors
which
are
to
increase
the
gains
of
the
second
stage
transistors Q203 and Q204 and to improve the linearity.
swi303-A |seor
To
©
C)
(
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|
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| a
|
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S O
_ Osw
' swi303-B | 5302 i
R304 R3
H i
et : eo ee
Q201,Q202 2S5k68A Q203 ~Q206
|
2SA841BL VUTING
LOUDNESS
IC OUTPUT CIRCUIT (See Figure 10)
When replacing it, be sure to apply silicone grease on the
surface of IC which is in contact with the heat sink, evenly
and as sparingly as possible.
Figure 10
ADJUSTMENT OF MAIN AMP CIRCUIT (See Figurel1 and 12)
. Check the power supply voltage.
l - Check that the potential between K706 and earth is
2. Set the power switch SW901 to “ON” position. +39V.
3. Set the volume control to “0” position. - Check that the potential between K708 and earth is
4. -Check that the potential between the test point TP] —39V.
and KSO1 is 12mV to 60mV.
- Check that the potential between the test point TP2 5. By using a signal generator (1kHz, 300mV), apply
and K502 is 12mV to 60mV. signals to the terminal AUX located at the rear of the
- Check that the potential between K501 and earth is set and adjust the volume control and balance control
in the range of +5OmV to —50mV so that the output signal of the speaker terminal (A or
- Check that the potential between K502 and earth is B) becomes 1W=2.0V. (See Figure 11)
in the range of +5OmV to —SOmV. 6. Adjust VR601 (and/or VR602) so that the left channel
- Check that the potential between Q307 emitter and output meter (and/or the right channel output meter)
earth is +20V. will indicate 1W.
-Check that the potential between Q308 emitter and
earth is —20V.
SIGNAL
GENERATOR ATTENUATOR
SPEAKER VTVM
TERMINAL
OSCILLOSCOPE
8 ohm
DUMMY
RESISTOR
Figure 11
Figure 12