Hitachi I-28 Service Manual page 7

SOUND DET.
T402
+B
SOUND IF INPUT
T 403
SIF AMP.
LIMITTER
(Circuit operation)
The detection circuit has a modified composition of the
ratio detection circuit; it operates as FM detection for the
amplified
second sound
intermediate
frequency signal.
Detected
signals enter the low-frequency
amplifier circuit
through the buffer amplifier. The audio-frequency amplifier
circuit consists of.a audio drive stage and a audio output
stage of the quasi-complementary SEPP OTL circuit; it
amplifies detected small sound signals to sufficiently large
signals which can drive a speaker.
EARPHONE
JACK
grace
ed
DE-EMPHASIS
R402
VOLUME
circuit.
The oscillating circuit is a RC oscillating circuit which
oscillates according to the time constant determined by
C605, R603, and R604. Synchronization is obtained from
output of the synchronizing amplifer. Output of the
oscillator is a pulse comes out in terminal a, and a
sawtooth-type wave form is made by C606 and R6O5. This
sawtooth-type wave performs correction of size linearity in
the wave form shaping circuit, and is then impressed on the
output amplifier circuit from terminal a3).
The output amplifier circuit is a Class B OTL current,
voltage feedback amplifier circuit which already has been
proven on the SV chassis. The output signal is obtained in
terminal @), supplying a sawtooth-type wave form current
to the deflecting yoke.
—FT-